Which sentence needs revision to fix a grammar error?

Read the paragraph.

(1) The concerns about sending people to Mars is definitely worth considering. (2) For one thing, the mission will cost billions of dollars. (3) This would be a huge additional cost at a time when national debts continue to skyrocket. (4) Also, that money could help fix problems here on Earth.

A. Sentence 1 should be revised to change “is” to “are.”
B. Sentence 2 should be revised to change “will cost” to “costs.”
C. Sentence 3 should be revised to change “continue” to “continued.”
D. Sentence 4 should be revised to change “could help” to “helps.”