This is our school. ____________ way, pl

乳牙上前牙散在间隙称为（）

A.可用间隙

B.灵长间隙

C.替牙间隙

D.发育间隙

E.必须间隙

工程项目的初步设计应在工程项目的( )阶段完成。

A．策划和决策

B．准备

C．实施

D．竣工验收和总结评价

水丸起模、盖面或包衣用药粉应过（）

A.3～4号筛

B.4～5号筛

C.5～6号筛

D.6～7号筛

E.8～9号筛

生石灰遇水消化成（）。

A.CaCO₃

B.Ca（OH）₂

C.CaO

请根据下面短文回答下列题：
Safety Rules for Bike-Riding.
1. Never ride out into a street without stopping first.
2. Watch for stop signs.
3. Look behind before turning or changing lanes (车道) .
4. Always ride on the right.
5. Never follow another rider without applying the rules.
Remember, your bicycle is a small compared with cars and trucks. It is not easily seen on crowded streets and will seldom attract attention on its own. At all times, do everything you can to make sure you are noticed.

When do bike-riders look behind
[A] Before they ride out into a street.
[B] Before they see stop signs.
[C] Before they make turns.