煤矿井下，严禁用铜丝、铁丝、铝丝代替保险丝。（）
参考答案：对
He was so deep in thought，thinking of the problem ________ he knocked into the tree without noticing it.
A．when
B．while
C．because
D．that
( )不属于装饰材料。
A．天然石材 B．水玻璃C．建筑陶瓷制品 D．装饰砂浆
