Question

 (2011年南通一模)________there are living creatures in the outer space as those on Earth hasn’t been proved until now.

A．How                     B．When

C．Where                   D．Whether

Answer 1

解析：選D�？疾槊�詞性從句。句意：外太空是否存在像地球上一樣的生物還不能確定。whether引導主語從句。