Giả thiết: Nhôm tác dụng với Fe₃O₄ chỉ tạo Al₂O₃ và sắt. Trộn 10,8g bột Al với 34,8g bột Fe₃O₄ rồi tiến hành phản ứng nhiệt nhôm trong điều kiện không có không khí. Hòa tan hoàn toàn hỗn hợp rắn sau phản ứng bằng dung dịch H₂SO₄ loãng dư thu được 10,416 lít khí H₂ (đktc). Hiệu suất của phản ứng nhiệt nhôm là:

A. 80,0%                       

B. 90,0%                    

C. 70,0%                    

D. 60,0%

Swim, Cycle, and Run

For athletes who like to (23) _____ a variety of endurance sports in a single race, triathlons are a great fit. These competitions (24) _____ running, cycling, and swimming into one race, and they take place one after the other in a single continuous timed race. Athletes who participate  must be in top physical form and have the skills needed to complete each portion of the race.

Training for triathlons means the athletes have to become proficient not only in the sport required in each stage, but they also have to become familiar with what (25) _____ from one to the other does to their bodies. Many inexperienced triathletes are surprised to (26) _____ hard it can be to switch from swimming to cycling to running, and how tired their muscles can suddenly feel,

         One thing all triathletes can agree (27) _____ is that no one ever told them that running a triathlon would be easy.

Điền vào số (23)

A. compete 

B. compete in       

C. contest    

D. take part

Mark the letter A, B, C, or D to indicate the correct answer to each of the following questions.

 The local residents suspected the authorities  ______ having kept the pollution level secret from the local people.

A. about

B. on

C. of

D. for