pp3_1*256

redhat158

求問A 的 it is known 有錯嗎? 為什麼不選呢? (正確C)

Scientists  have dated sharp-edged flakes of stone found in the fine-grained sediments of  a dry riverbed in the Afar region of Ethiopia to between 2.52 and 2.60  million years ago, pushing back by more than 150,000 years the earliest date when it is known that humans made stone  tools.

A. when  it is known that humans made

B. at  which it is known that humans had made

C. at  which humans are known to have made

D. that  humans are known to be making

E. of humans who were known to make

栖叶泠风

A中的it指代很模糊，而且when it is known的表达很繁琐，C用宾语从句表达比A更简洁