Theyaregoingdowntownbusinsteadoftheirbikes

Question

They are going downtown _bus instead of _their bikes

Answer 1

1.by
2.riding
全句：They are going downtown by bus instead of riding their bikes.
分析：
1,by bus是个固定词组,意思是乘公共汽车；
2,instead of 后接名词或动名词,因为物主代词前面不能是名词,所以只能是动名词.根据句子意思,这个词组应该是“骑他们的自行车”的意思,所以用riding(ride 的现在分词形式）.