You will be given a definition of a task first, then an example. Follow the example to solve a new instance of the task.
In this task, you're given a question, along with a context passage which has extra information available on certain terms mentioned in it. Your job is to determine which sentence(s) from the passage can be used to search for further information needed to answer the question.

Question: When did the operation during which the 704th dropped supplies to allied troops near Nijmegen begin? Passage: The group was occasionally diverted from strategic missions to carry out air support and interdiction missions. It supported Operation Overlord, the invasion of Normandy by attacking transportation targets, including bridges, along with airfields and strong points in France. On D Day, the squadron and the rest of the 446th Group led the first heavy bomber mission of the day. The 446th aided ground forces at Caen and Saint-Lo during July by hitting bridges, gun batteries, and enemy troops. During Operation Market Garden, the attempt to seize a bridgehead across the Rhine in the Netherlands, the 704th dropped supplies to allied troops near Nijmegen. It struck lines of communications during the Battle of the Bulge. During Operation Varsity in March 1945, it supplied ground and airborne troops near Wesel. The squadron flew its last combat mission on 25 April 1945 against Salzburg, Austria. The group had flown 273 missions and had lost 58 aircraft during the war,
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Solution: During Operation Market Garden, the attempt to seize a bridgehead across the Rhine in the Netherlands, the 704th dropped supplies to allied troops near Nijmegen.
Why? The passage describes the 704th's actions during Operation Market Garden.

New input: Question: How long had the Taff Vale Railway been in existence the year it was extended to Cymmer? Passage:In 1809, Walter Coffin sunk the first coal pit in the Rhondda, further up the valley in Dinas, but a lack of a transportation network greatly affected the profitability of coal mining as an industry in the region. Coffin tackled this problem by constructing a one-mile tramline which connected his mines in Dinas to a tramline built by Dr. Richard Griffiths at Denia (Pontypridd), which linked to a private canal that joined onto the Glamorganshire Canal at Treforest. Coffins tramline followed the southern bank of the River Rhondda and ran through Porth. The existence of the tramline made the development of the Porth and Cymmer region far more attractive, and by the middle of the 19th century there was an impetus to expand coal mining in the area. In 1841 Richard Lewis joined Coffin in trying to exploit the region with his level built at Cymmer. This resulted in the construction of around fifty miners' cottages, several of which were located in Porth. In 1844 Lewis Edwards of Newport and George Gethin of Penygraig opened a small level at Nyth-bran on the eastern borders of Porth, the villages' first coal mine. This was followed in 1845 by the sinking of the Porth Colliery by David James of Merthyr, the success of which saw him build the Llwyncelyn Colliery in 1951, also in Porth. By 1850 the Taff Vale Railway had been extended to Cymmer replacing the tramline, allowing direct access between the lower Rhondda and the ports of Cardiff.

Solution:
By 1850 the Taff Vale Railway had been extended to Cymmer replacing the tramline, allowing direct access between the lower Rhondda and the ports of Cardiff