— Why does the boy keep crying?
— It is he has lost his favorite car model.
A. since
B. so
C. when
D. because
网友回答
A. since
B. so
C. when
(答案→)D. because
解析：考查连词：A. since自从，B. so所以，C. when当,…时候，D. because因为，句意：为什么这些男孩一直在哭？--是因为他失去了最喜欢的汽车模型。Because引导表语从句，回答why的问题。选D。