碗扣式钢管脚手架中的重型架一般取较大的立杆纵距，用于重载作业或作为高层外脚手架的底部架。（）
参考答案：错
Mark Twain worked for several years as a pilot on a steamboat, taking passengers up and
down the Mississippi, the great river ___flows from the north of the US near the Canadianborder.
A．as
B．what
C．which
D．who
使用绝缘操作杆时，工作人员可以不戴绝缘手套。
