重大危险源分几级？
参考答案：
一级重大危险源；二级重大危险源；三级重大危险源；四级重大危险源。
—_________T-shirt do you like better, the red one or the blue one?
—I prefer the red one.
A．How much
B．How many
C．Whose
D．Which
简述消除间隙效应的措施。
