Question: The St. Louis, San Francisco and Texas Railway (SLSF), was a subsidiary railway to the St. Louis-San Francisco Railway, in 1980 it merged into which United States-based railroad company formed from a merger of four major U.S. railroads?

Context paragraphs:
Pacific Railroad: The Pacific Railroad was a railroad based in the U.S. state of Missouri.  It was a predecessor of both the Missouri Pacific Railroad and St. Louis-San Francisco Railway.

St. Louis-San Francisco Railroad Depot: St. Louis-San Francisco Railroad Depot is a historic train station located at Poplar Bluff, Butler County, Missouri.  The station was built in 1928 by the St. Louis–San Francisco Railway.  It is a one-story, Mission Revival style brick building sheathed in textured stucco.  It sits on a concrete foundation, has a gable and hipped Spanish tile roof, and features two interior brick and stucco chimneys.  The building is presently occupied as a railroad museum.

Atlantic and Pacific Railroad: The Atlantic and Pacific Railroad was a U.S. railroad that owned or operated two disjointed segments, one connecting St. Louis, Missouri with Tulsa, Oklahoma, and the other connecting Albuquerque, New Mexico with Southern California.  It was incorporated by the U.S. Congress in 1866 as a transcontinental railroad connecting Springfield, Missouri and Van Buren, Arkansas with California.  The central portion was never constructed, and the two halves later became parts of the St. Louis-San Francisco Railway and Atchison, Topeka and Santa Fe Railway systems, now both merged into the BNSF Railway.

Burlington Northern Railroad: The Burlington Northern Railroad (reporting mark BN) was a United States-based railroad company formed from a merger of four major U.S. railroads.  Burlington Northern operated between 1970 and 1996.

Texas Special: The Texas Special was a named passenger train operated jointly by the Missouri-Kansas-Texas Railroad (also known as the MKT or the Katy) and the St. Louis-San Francisco Railway (the Frisco).  It was the flagship of both these lines, operating between St. Louis, Missouri, and San Antonio, Texas, from 1915 until 1959, after which time the Katy changed the northern destination from St Louis to Kansas City after the Frisco discontinued service from St. Louis.

Arkansas Valley and Western Railway: The Arkansas Valley and Western Railway (AV&W) was built as a short line railroad operating within the U.S. state of Oklahoma.  It was founded in 1902 to link the city of Tulsa with the main transcontinental line of the Atchison, Topeka and Santa Fe Railway (AT&SF) at Avard.  The line was built in sections, initially from AV&W Jct.  (West Tulsa) to Steen (Enid) during 1902-03.  In 1904 it was extended westward to the junction with AT&SF at Avard.  On July 19, 1907, the railroad was purchased by the St. Louis-San Francisco Railway (the "Frisco"), who operated it until November 21, 1980, when the Frisco was acquired by Burlington Northern Railroad.

Meteor (train): The Meteor was a named passenger train operated by the St. Louis-San Francisco Railway (a.k.a. SLSF or "the Frisco").  It ran overnight between Oklahoma City and St. Louis via Tulsa and was later extended to Lawton, Oklahoma on July 18, 1955.  The name was shared with a branch line "Meteor" running between Monett, Missouri, and Paris, Texas.  Later this line was truncated to terminate at Fort Smith, Arkansas.  These Frisco trains should not be confused with Amtrak's "Silver Meteor".

St. Louis, San Francisco and Texas Railway: The St. Louis, San Francisco and Texas Railway (reporting mark SLSF) was a subsidiary railway to the St. Louis-San Francisco Railway (Frisco) operating 159 miles of railway line in Texas.  The Frisco, including the subsidiary, formed a large X-shaped system across the states of Kansas, Missouri, Oklahoma, Texas, Arkansas, Mississippi and Alabama.  It merged into SLSF at the beginning of 1964; SLSF merged into the Burlington Northern Railroad in 1980.

Kansas City, Clinton and Springfield Railway: The Kansas City, Clinton and Springfield Railway, also known as the Leaky Roof Railway, is a now abandoned rail line that ran from Olathe, Kansas, near Kansas City, through Clinton, Missouri, and on to Ash Grove, Missouri, where it tied in with the Kansas City, Fort Scott and Gulf Railway, later the Frisco Railroad.  A short branch line served Pleasant Hill, Missouri.  It was founded in 1884, as a subsidiary of the KCFS&G; on February 12, 1885, the railroad was incorporated in Missouri.  The line was later bought by the Frisco (St. Louis-San Francisco Railway) in 1928.  After consolidation with the Frisco, the route was deemed redundant to the parallel and better constructed Frisco "Highline".  Seeking to cut costs, the Frisco chose to abandon the line in 1934.  Because it ran parallel to the Frisco's Highline, the two railroads intersected at many places.  Thus, the Frisco chose to consolidate the two lines into one by keeping the track of whichever railroad had the favorable route between these numerous crossings.  The less favorable sections were then removed.  Service continued over these portions of the line with a daily except Sunday local until the mid-1970s, when dam construction and bridge fires ended through service on the route between Kansas City and Springfield, Missouri.  Operating for a while as a North and South branch line, services were cut and the line was, section by section, successively abandoned.  Although the rails are now gone, traces can be found along Route 7 and Route 13, however along most sections, little remains to be seen.

Fred Harvey (entrepreneur): Frederick Henry Harvey (June 27, 1835 – February 9, 1901) was an entrepreneur who developed the Harvey House lunch rooms, restaurants, souvenir shops, and hotels, which served rail passengers on the Atchison, Topeka and Santa Fe Railway, the Gulf Coast and Santa Fe Railway, the Kansas Pacific Railway, the St. Louis-San Francisco Railway, and the Terminal Railroad Association of St. Louis.

Supporting paragraphs: St. Louis, San Francisco and Texas Railway Burlington Northern Railroad
Answer: Burlington Northern Railroad