Question: The Ironton Railroad became part of which Class 1 Railroad Corporation?

Context paragraphs:
Fall River Railroad (1846): The Fall River Railroad was incorporated in 1846 as a merger between the Fall River Branch Railroad, the Middleborough Railroad Corporation and the Randolph & Bridgewater Railroad Corporation.  The railroad ran from Fall River through Middleborough and Bridgewater to South Braintree where it connected to the Old Colony Railroad line.

Southern Railway (U.S.): The Southern Railway (reporting mark SOU) (also known as Southern Railway Company and now known as the current incarnation of the Norfolk Southern Railway) is a name of a class 1 railroad that was based in the Southern United States.  The railroad is the product of nearly 150 predecessor lines that were combined, reorganized and recombined beginning in the 1830s, formally becoming the Southern Railway in 1894.

Ironton Rail Trail: The Ironton Rail Trail is a rail trail that spans 9 miles in Lehigh County, Pennsylvania.  The trail was made from tracks of the defunct Ironton Railroad and includes a paved 5 mile loop.

Fall River Branch Railroad: The Fall River Branch Railroad was incorporated in Massachusetts in 1844, to provide a rail link from the emerging textile town of Fall River to the New Bedford and Taunton Railroad at Myricks Junction.  It began operating in 1845 with 12 miles of track.  A year later, in 1846 it merged with the Middleborough Railroad Corporation and the Randolph & Bridgewater Railroad Corporation to become the Fall River Railroad Company, with a new connection to Bridgewater.  It operated as the Fall River Railroad until 1854 when it merged into the Old Colony Railroad to become the Old Colony and Fall River Railroad Company.

National highways of Japan: Japan has a nationwide system of national highways (一般国道 , Ippan Kokudō ) distinct from the expressways.  The Ministry of Land, Infrastructure, Transport and Tourism and other government agencies administer the national highways.  Beginning in 1952, Japan classified these as Class 1 or Class 2.  Class 1 highways had one- or two-digit numbers, while Class 2 highways had three-digit numbers.  For example, Routes 1 and 58 were Class 1 highways while 507 (the one with the highest number) was a Class 2 highway.

Tecumseh Branch Connecting Railroad: The Tecumseh Branch Connecting Railroad is a railroad originally built by the Detroit, Toledo and Ironton Railroad.

Detroit, Toledo and Ironton Railroad: The Detroit, Toledo and Ironton Railroad (reporting mark DTI) operated between its namesake cities of Detroit, Michigan and Ironton, Ohio via Toledo between 1905 and 1983.  At the end of 1970 it operated 478 miles of road on 762 miles of track; that year it carried 1244 million ton-miles of revenue freight.

Conrail: Conrail, the Consolidated Rail Corporation, (reporting mark CR) , was the primary Class I railroad in the Northeastern United States between 1976 and 1999, when its routes were split between the CSX Corporation and Norfolk Southern Railway.  Conrail, a portmanteau of "consolidated" and "rail" from the name of the company, operates now as a joint-subsidiary for some limited functions.

Ironton Railroad: The Ironton Railroad was a shortline railroad in Lehigh County, Pennsylvania.  Originally built in 1861 to haul iron ore and limestone to blast furnaces along the Lehigh River, traffic later shifted to carrying Portland cement when local iron mining declined in the early 20th century.  Much of the railroad had already been abandoned when it became part of Conrail in 1976, and the last of its trackage was removed in 1984.

Delaware, Lackawanna and Western Railroad: The Delaware, Lackawanna & Western Railroad (or Delaware, Lackawanna & Western Railroad Company and also known as the DL&W or Lackawanna Railroad) was a U.S. Class 1 railroad that connected Buffalo, New York, and Hoboken, New Jersey, a distance of about 400 mi .  Incorporated in 1853, the DL&W was profitable during the first two decades of the twentieth century, but its margins were gradually hurt by declining traffic in coal and competition from trucks.  In 1960, the DL&W merged with rival Erie Railroad to form the Erie Lackawanna Railroad.

Supporting paragraphs: Ironton Railroad Conrail
Answer: Conrail