Heat evil was occurring. "My son made it about 100 yards from the river and then dropped," says his father, Robin. Two boys of them raced to the river to get him water.

　　When the boys arrived, the last rafting (筏运) trip of the day was passing by. As luck would have it, among the waiting riders were a few doctors. They rushed to give David first aid before going for help. But it was too late. David passed away from the heat evil.

　　It's been 21 years since the boy's death, and hiking still holds a strong memory of David for his family. The summer before the tragedy, his father had a long time to devote to his family. David and his dad spent the summer hiking all over the High Uintas, where snow-topped peaks reflect tower over glacier(冰川)formed lakes.

　　The photo Robin took of Christmas Meadows there won the Reader's Digest "From Sea to Shining Sea" photo contest and appeared on the July 2017 magazine cover. To Robin, it isn't just a fascinating landscape - it's also a powerful reminder of his late son.

28. How many people does David's group consist of?.

A. 11 B.10 C.9 . D.8

29. What does the sentence "Even the leaders were having trouble walking on." in Paragraph 3 suggest?

A. The leaders were taller and older.

B. The leaders covered shorter distance.

C. The leaders were healthier and stronger.

D. The trouble the group faced was so great as to be beyond expectation.

30. Where did Robin take the photo which won the Reader's Digest "From Sea to Shining Sea" photo contest？

A. On the High Uintas. B. Where David had been to.

C. In the Grand Canyon. D. In the Christmas Meadows.

31. What does the passage intend to tell us mainly?

A. Take enough water with you when hiking.

B. Don't hike to the Grand Canyon in too hot weather.

C. Robin still misses his late son, David.

D. Doctors can't necessarily succeed in saving every patient.

D

　　Since the sex of a sea turtle（海龟） is determined by the heat of sand hatching the eggs, scientists had suspected they might see slightly more females. Climate change, after all, has driven sea temperatures higher, which, in these creatures, favors female children. They found female sea turtles from Raine Island, the Pacific Ocean's largest and most important green sea turtle living area, now outnumber males by at least 116 to 1. "This is extreme," says turtle scientist Camryn Allen.

Biologist Michael Jensen wanted to know if climate change had already changed turtles' sexes. By using genetic(基因的) tests, he'd figured out that he could follow turtles of all ages. Still, his research data would lack an important detail: sex. Only after a turtle matures is it possible to tell its sex from the outside -mature males have slightly longer tails. By then turtles can be decades old, so scientists often use laparoscopy(腹腔镜检查)，sending a thin tube into each animal, but that's not so practical if you are hoping to examine hundreds of creatures. Fortunately, at a turtle