Which statement best explains why the transcontinental railroad took several years to build? Digging through mountains was difficult, and harsh weather slowed progress. Several Civil War battles took place nearby and kept work from progressing. Congress fought over funding for the railroad, leading to work stoppages. Immigrants were not interested in railroad work, which made it hard to fill jobs.

Digging through the mountains was very difficult, and the long winters hampered workers' ability to make progress.

Digging through mountains was difficult, and harsh weather slowed progress.

Explanation:

The cross-country railrold took quite a while to build because burrowing through the mountains was troublesome, and the long winters hampered worker's ability to gain ground. The lower regions of Sierra Nevada, the winter snowtorms, lack of solid work and expanding requirement for burrowing hampered the advancement as they went higher in the mountains.