保存煤样的房间应有热源，以防氧化。
参考答案：错
----What time do you start work?
---- _____________.
A．It’s none of your business.
B．It varies.
C．From 8 a.m. to 4 p.m.
D．It doesn’t make any difference
形式运算阶段的思维方式有哪些特征?
