Complex sentence: A 7 miles long standard gauge line was built in 1974 from the power plant to the Hosteen stockpile, which was expanded to the present 14 miles in 1983.
Split into simpler sentences: A 7 miles long standard gauge line was built in 1974 from the power plant to the Hosteen stockpile. The line was expanded to the present 14 miles in 1983.