Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that best combines each pair of sentences in the following questions.

I work harder than before. I get better grades.

A. The possibility of changing the Martian environment

B. The challenge of interplanetary travel

C. The advantages of establishing colonies on Mars

D. The need to study Martian ecology

B. lacks

C. hopes

D. neglects

A. appealing

B. committed

C. specialized

D. admitted

A. has read / make

B. was reading/made

C. had read/made

D. read / had made

A. humanity

B. civilization

C. constitution

D. philosophy

A. hadn't received / moved

B. don't receive / had moved

C. didn't receive / have moved

D. haven't received/moved