Mark the letter A, B, C, or D on...

Câu hỏi: Mark the letter A, B, C, or D on your answer sheet to indicate the underlined part that needs correction in each of the following questions.
Some methods to prevent soil erosion are plowing parallel with the slope of hills, to plant trees on unproductive land, and rotating crops.

A. Some

B. to prevent

C. are

D. to plant