一般地，在相同条件下的易燃液体，其闪点比燃点（）。A．低 B．高 C．二者相等 D．

Having reached the highest point of our route according to plan, we discovered something the map had not told us. It was impossible to climb down into the Kingo valley. The river lay deep between mountain sides that were almost vertical（垂直）.We couldn’t find any animal tracks, which usually show the best way across country, and the slopes were covered so thickly with bushes that we could not see the nature of the ground. We had somehow to break through to the river which would give us our direction out of the mountains into the inhabited lowlands.

Our guide cut a narrow path through the bushes with his long knife and we followed in single file. Progress was slow. Then, when we thought we had really reached the river, we found ourselves instead on the edge of a cliff with a straight drop of 1,000 feet to the water below. We climbed back up the slope and began to look for another way down. We climbed slipped, sweated and scratched our hands to pieces and finally arrived at the river. Happily we came downhill along its bank without having to cut our way. However, after a few miles the river entered a steep-sided gap between rocks and suddenly dropped thirty-five feet over a waterfall. There was no path alongside it and no way round it.

Then one of the guides saw a way of overcoming the difficulty. There was a fallen tree lying upside down over the waterfall with its leafy top resting on the opposite bank below the falls. Without hesitation he climbed down the slippery trunk to show us how easy it was. Having got to the fork of the tree, he moved hand over hand along a branch for four or five feet with his legs hanging in space, then he dropped onto the flat bank the other side, throwing his arms in the air like a footballer who has scored goal, and cheerfully waving us on.

74．Having reached the highest point on their route, the travelers expected to be able to    .

A．track animals to the river

B．put away the maps they had been using

C．come near to the river from a different direction

D．get down to the river without much difficulty.

75．The travelers wanted to get to the river because      .

A．it would lead them to the waterfall

B．it would show them which way to go

C．it was the only possible way out of the mountains

D．it was a quicker way than going over the mountains

76．One reason why the travelers took so long to get to the river was that      .

A．it was too hot to move quickly

B．there was no proper path

C．they all tried to go different ways

D．they could not follow the animal tracks

77．To get past the waterfall the guide had to      .

A．use a fallen tree as a kind of bridge

B．cross the river above the waterfall

C．slide down a steep river bank

D．swing across the river from a high branch

皮肤由哪个胚层分化而来

A．外胚层
B．中胚层
C．内胚层
D．外胚层和中胚层
E．中胚层和内胚层

由于设备工程的复杂性，设备监理人员难以对设备工程各阶段的所有相关工作进行监督和控制。而且，传统的进度控制方法通常是从施工单位角度提出的，对监理单位实施的监督和管理任务并不完全适用，设备监理工程师有必要( )。

A．对设备工程进度实行动态直接控制

B．进行设备工程的主要相关单位分析

C．建立设备工程进度报告制度

D．制定工程拖期的申请与审批工作程序

马氏体是碳在α－Fe中的（）固溶体。

A.饱和

B.不饱和

C.过饱和

松开螺钉和定位螺丝，向左面推动带有烟舌的支座，使烟舌前端位于烟枪槽中间并伸入（）mm，拧紧螺钉，然后把烟舌支座退回约5mm，拧紧滚花螺母和转动定位螺丝抵触到双头螺栓。

A、5

B、10

C、12

D、15