柴油发动机进气冲程进入气缸的是（）。
A.柴油和空气的可燃混合气
B.纯空气
C.根据需要而定
参考答案：B
牙石致病机制中最主要的是
A．压迫牙龈B．妨碍口腔卫生的保持C．吸附细菌毒素D．粗糙表面的机械刺激E．牙石表面未钙化的菌斑
—There _ a concert this evening.
—Yeah! Exciting news!.[ ]
A. are going to be
B. is going to be
C. is going to have
D. will have
