实践表明，风机或泵类负载恒速运转改为变频调速后，节能可达（）。
A、5%~10%
B、10%~20%
C、20%~30%
D、30%~40%
参考答案：D
单句改错。
1. This is (A) his (B) the best (C) book (D).
2. He is (A) taller (B) than (C) any boy (D) in his class.
3. Which (A) do you like (B) best (C), this one or (D) that one?
4. Mike is (A) very (B) cleverer (C) than (D) Jack.
5. Kate draws (A) best (B) of (C) her class (D).
睫状肌收缩时（）
A.睫状小带紧张，晶状体变凸，适于看近物
B.睫状小带紧张，晶状体变平，适于看远物
C.睫状小带紧张，晶状体变平，适于看近物
D.睫状小带放松，晶状体变凸，适于看近物
E.睫状小带放松，晶状体变平，适于看远物
