Viết số: 1005 (theo mẫu)

Thổi khí  CO 2  vào dung dịch chứa 0,02 mol  Ba ( OH ) 2 , thu được m gam kết tủa. Biết số  0 , 005 ≤ n CO 2 ≤ 0 , 024  Giá trị của m là :

A.  0 < m ≤ 3 , 94

B.  0 < m ≤ 0 , 985

C.  0 , 985 ≤ m ≤ 3 , 94

D.  0 , 985 ≤ m ≤ 3 , 152

Cho phản ứng hóa học: Fe + CuSO4 → FeSO4 + Cu

Trong phản ứng trên xảy ra

A. sự oxi hóa Fe và sự oxi hóa Cu

B. sự khử Fe²⁺ và sự oxi hóa Cu

C. sự oxi hóa Fe và sự khử Cu²⁺

D. sự khử Fe²⁺ và sự khử Cu²⁺

 Read the following passage on transport, and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 43 to 50.

In addition to the great ridges and volcanic chains, the oceans conceal another form of undersea mountains: the strange guyot, or flat-topped seamount. No marine geologist even suspected the existence of these isolated mountains until they were discovered by geologist Harry H. Hess in 1946.

He was serving at the time as naval officer on a ship equipped with a fathometer. Hess named these truncated peaks for the nineteenth-century Swiss-born geologist Arnold Guyot, who had served on the faculty of Princeton University for thirty years. Since then, hundreds of guyots have been discovered in every ocean but the Arctic. Like offshore canyons, guyots present a challenge to oceanographic theory. They are believed to be extinct volcanoes. Their flat tops indicate that they once stood above or just below the surface, where the action of waves leveled off their peaks. Yet today, by definition, their summits are at least 600 feet below the surface, and some are as deep as 8,200 feet. Most lie between 3,200 feet and 6,500 feet. Their tops are not really flat but slope upward to a low pinnacle at the center. Dredging from the tops of guyots has recovered basalt and coral rubble, and that would be expected from the eroded tops of what were once islands. Some of this material is over 80 million years old. Geologists think the drowning of the guyots involved two processes: The great weight of the volcanic mountains depressed the sea floor beneath them, and the level of the sea rose a number of times, especially when the last Ice Age ended, some 8,000 to 11,000 years ago.

According to the passage, most guyots are found at a depth of _____.

A. between 600 and 3,200 feet         

B. more than 8,200 feet

C. less than 600 feet                

D. between 3,200 and 6,500 fee