When the boulders are made of rock that is different from the bedrock which

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Mark the letter A, B, C or D on your answer sheet to indicate the underlined part that needs correction in each of the following questions

When the boulders are made of(A) rock that is different from the bedrock which(B) they(C) or the soil of the field rests, they are called(D) erratics

are made of

which

they

are called

Giải thích

Đáp án : B

“has been never” -> “has never been”. Sai vị trí của trạng ngữ, “never” phải đứng giữa “has/have” và động từ