过共析钢和共析钢的淬火加热温度为（）。

（2分）如图所示的光现象中，可用光的反射原理解释的是（　　）

5. “Was his father very strict with him when he was at school?” “Yes. He had never praised him _______ he became one of the top students in his grade.”

A．after

B．unless

C．until

D．when

局限性青少年牙周炎的临床表现之一是（）

A.多发生于青少年男生

B.早期口腔不清洁

C.好发于第一磨牙和上下切牙

D.牙槽骨水平吸收

E.以父系遗传较多

如何针对林木病害进行林业技术防治？

地物波谱特征