调试烟气挡板前,必须用()的方式操作各烟气挡板,挡板应开关灵活,开关指示及反应正确。
A、远程控制;
B、就地手动;
C、就地气(电)动;
D、上述三种。
参考答案:D
如图,点E是∠AOB的平分线上一点,EC⊥OA,ED⊥OB,垂足分别为C、D.
(1)求证:∠ECD=∠EDC;
(2)若∠AOB=60°,OE=8,试求EF的长.
In our school, every student had free _______ to the library.
A.access
B.chance
C.right
D.use