Question

which sentence uses a comma correctly? a if new research proves correct, people may be able to grow rice on mars. b scientists have been hoping to grow food since, they decided to go to mars. c rice is an excellent crop to grow because, it is healthy and easy to prepare. d scientists will continue doing research, and hope to achieve great results.

Explanation:

1. In option A, the comma is used correctly to separate the dependent - clause "If new research proves correct" from the independent - clause "people may be able to grow rice on Mars".
2. In option B, the comma after "since" is incorrect as "since they decided to go to Mars" is a subordinate clause and doesn't require a comma after "since".
3. In option C, the comma after "because" is incorrect. "Because it is healthy and easy to prepare" is a subordinate clause and doesn't need a comma after "because".
4. In option D, the comma before "and" is incorrect in a simple compound - predicate sentence like this. There is no need for a comma when the subject "Scientists" is the same for both verbs "continue" and "hope".

Answer:

A. If new research proves correct, people may be able to grow rice on Mars.