牙周病的病因，正确的是()A．菌斑可引起牙周病 B．食物嵌塞可引起牙周病 C．全身疾

一种商品提价10%后，销量大减，于是商家又降价10%出售．现在的价格比最初的价格降低．______．

I wonder ____ made your English teacher so angry in her class this morning.

A   what was it that  B how was it that  C what it was that  D how it was that

对氟吸收较强的树种有（）、（）、（）等。

油机不出油或者出油量少应是（）发生故障.

粗略估测下图卡尺（200mm，精度为0.02mm）所示，下列尺寸接近的是（）

A.28.60mm

B.30.60mm

C.30.10mm