热机的工作“特点”是：燃料的______能通过燃烧转化为______能，又通过做

当施工期间最高气温超过30℃时，水泥砂浆和水泥混合砂浆应分别在拌成后( )内使用完毕。

A．2h和3h
B．3h和4h
C．3h和2h
D．4h和3h

第二节根据对话内容，从对话后的选项中选出能填入空白处的最佳选项.选项中有两项多余选项. （共5小题，每小题1分，满分5分）( 答案涂在答题卡71-75的位置)

一welcome back!I didn’t see you in the history class on Friday．

一__61__．My geography class went on a field trip to look at some of the different rocks．   

一Really? ___62__!Where did you go?  

一A desert.It gets hot during the day，but it cools off very quickly at night． ___ 63__.

—Well，did you enjoy the trip?

--Of course I did．Since there are so few plants growing there，it’s very easy to see different rocks．

— ___64___．You must call me if you have the Chance to go there again.

一No problem． _65__ .

A．I really want to go there

B．That sounds excellent

C．I will be your guide next time

D．It is very dry there after the sun goes downE．I’m tired of this trip

F．I wasn’t here on Friday

G．We learnt a lot from this trip

Mapleson系统属于下列哪一种（）

A.开放系统

B.半开放系统

C.紧闭系统

D.半紧闭系统

E.T形管装置系统

海水温度高时海水淡化装置真空度下降可能是因为（）。

A.海水含气量增多

B.冷却能力下降

C.喷射泵抽气能力降低

D.B+C