单面梯子的架设与地面夹角以（）为宜。
A、35～45°
B、45～55°
C、55～65°
D、65～75°
参考答案：D
(2013·咸阳二模)We should keep in mind that the earth is our only home and only by saving the environment________ourselves.
A．we can save
B．can we save
C．we must save
D．must we save
判别真假三三味的原则是什么？
