单项选择题
The red suitcase is expensive （） it is made of leather.
A. when B. if C. because
单项选择题 We have been good friends ______ we met at school.
单项选择题 They climbed higher （） they might get a better view of the city.
单项选择题 —Do you know ______ he came—Yes, I do. He came by car.
