A:to join;to speak
B:join;speaking
C:join;to speak
D:to join;speaking
金刚石、石墨和C60都是由碳元素组成的单质,下列说法中正确的是( )
《西游记》是我国四大名著之一,主要讲的是唐僧师徒四人历经“九九八十一难”去西天取经的神话故事。据此回答小题:
____ is very ____,but it is very difficult.