25.
(A) because
(B) due to
(C) account for
(D) owing to

21. (A) woods (B) wooded (C) woody (D) wooden

22. (A) aiming (B) aimed (C) to aim (D) with aim 

23. (A) can (B) canned (C) cans (D) canning

24. (A) linking (B) to link (C) is linked (D) linked

26. (A) how easy (B) how easy is it (C) how it is easy (D) how easy it is

27. (A) in (B) as (C) on (D) with.

28. The author indicates that Curiosity isn't looking for life itself because (A) it can't travel to Mount Sharp, where evidence of life is most likely to be found (B) the rapid temperature changes on Mars makes it impossible (C) the surface of Mars isn't hospitable to life anymore (D) the equipment Curiosity uses isn't advanced enough

29. The phrase stumbled on in paragraph 5 is closest in meaning to (A) discovered by chance (B) was slowed down by (C) worked on (D) passed by

30. The first rock that Curiosity examined did NOT indicate that (A) Mars once had liquid water on its surface (B) the rock contained possible sources of energy (C) microorganisms inhabited the pond where the rock formed (D) the rock contained the basic building blocks of living organisms

31. The author mentions the photographers William Henry Jackson and Ansel Adams in part because (A) The landscapes that they photographed resembled the ones that Curiosity photographed. (B) Their photos, like the ones taken by Curiosity, captured the public's imagination. (C) Like Curiosity, they employed the most advanced photographic technology available. (D) Their images inspired the engineers and scientists who designed and built Curiosity.