问题补充：
A girl on the bus begin to sing a pop song and soon all the other students .
A. majored in
B. joined in
C. came in
D. handed in
答案：
A. majored in
(答案→)B. joined in
C. came in
D. handed in
解析：短语辨析。A 以..为专业；B参加，加入；C进来；D上交；句意：公交车上一个女孩开始唱一首流行歌曲，很快所以其它的学生都加入进来了。故B正确。
