800 câu trắc nghiệm Điền từ Tiếng Anh có đáp án - Phần 22

They have been (4)_____ to swim up to 100 km, but when there is less ice, they may have to swim further and this can (5)_____ fatal to the bears. A number of bears have drown in the last few

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They have been (4)_____ to swim up to 100 km, but when there is less ice, they may have to swim further and this can (5)_____ fatal to the bears. A number of bears have drown in the last few years and scientists believe that it is because they were not able to reach more ice before they became too tired and couldn't swim any further.

known

learnt

experienced

noticed

Giải thích

A là đáp án đúng