Some students think that learning a foreign language is slow and difficult-think of all the hours of hard work ________ they have spent learning English．
A.when
B.in which
C.that
D.while
对258人提供帮助
Some students think that learning a foreign language is slow and difficult-think of all the hours of hard work ________ they have spent learning English．
A.when
B.in which
C.that
D.while
对258人提供帮助