The tank is safe to enter
The tank is especially dangerous to enter
Carbon monoxide is present
Water vapor present when the tank was sealed has oxidized
第1题：
A.have,,joined
B.have,,been
C.has,,joined
D.has,,been
第2题：
We are of course() that the period for completion of your project has already been exceeded .
A. know
B. to know
C. aware
D. sure
第3题：
A.since
B.for
C.before
D.after
第4题：
Which statement about entering into a tank which has been sealed for a long time is TRUE ________．
A.The tank should be tested only once to ensure the oxygen content is at least 14% before entry
B.The tank must be tested at frequent intervals to ensure that hazardous gasses have not regenerated
C.The tank need not be tested for oxygen content if it is ventilated for more than 24 hours
D.If the oxygen content tests at less than 12% you should wear an approved gas mask
第5题：
A tank has been sealed and unventilated(不通风的) for a long period of time. Which of the following conditions does this indicate?
A.The tank is safe to enter
B.The tank is especially dangerous to enter
C.Carbon monoxide(一氧化物) is present
D.Water vapor present when the tank was sealed has oxidized(使氧化)
第6题：
We can obviously notice that over a period of no practice what has been learned tends to be forgotten from______.
第7题：
A.had been cleaning
B.is cleaning
C.has been cleaning
D.was cleaning
答案：D
解析：本题考查时态用法。根据题干可知时态是过去时，故排除B、C两项。while是一个信号词，表示一个时间点，并不强调完成，排除A。句意：秘书在打扫桌子的时候，他发现了丢失已久的报告。
第8题：
A.has been reading
B.had read
C.is reading
D.read
第9题：
Which statement about entry into a space that has been sealed for a long time is TRUE ________．
A.A tank that has been used to carry hazardous liquids should be tested for oxygen content，toxicity，and explosive gases
B.You can safely enter the space without a breathing apparatus if the oxygen content exceeds 14%
C.The natural ventilation through the installed vents is sufficient to provide the proper oxygen content
D.The heat of the sun on upper ballast tanks，such as in a bulk carrier，may generate carbon monoxide
第10题：
When a non-volatile cargo is carried in a tank that has not been previously gas freed，then that tank shall ______．
A.be purged with hydrocarbon gas prior to loading
B.be gas-freed after loading operations
C.not be maintained in an inert condition
D.be maintained in an inert condition