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 fix problems here on earth.

which sentence needs revision to fix a grammar error?
sentence 1 should be revised to change “is” to “are.”
sentence 2 should be revised to change “will cost” to “costs.”
sentence 3 should be revised to change “continue” to “continued.”
sentence 4 should be revised to change “could ” to “