單項選擇題A tank has been sealed and unventilated for a long period of timeWhich 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 is present
D.Water vapor present when the tank was sealed has oxidized


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2.單項選擇題A tank which has been sealed for a long period of time can be dangerous because （）.

A.steel surfaces consume oxygen by rusting
B.sealed tanks usually form a vacuum
C.moisture condenses in the tank, displacing the oxygen
D.most tank coatings give off poisonous vapors in the presence of moisture

3.單項選擇題Records of garbage disposal are required to be maintained （）.

A.until each quadrennial PSC inspection
B.until the end of each voyage
C.for a minimum of one year
D.for a minimum of two years

4.單項選擇題The use of sinking and dispersing agents for the removal of surface oil is （）.

A.the most common method used in the United States
B.too expensive for common use
C.generally safe to sea life
D.generally harmful to sea life

5.單項選擇題One of the disadvantages of using carbon dioxide to extinguish a fire in an enclosed space is （）.

A.the "snow" which is sometimes discharged along with the gas is toxic
B.prolonged exposure to high concentrations of  C02 gas causes suffocation
C.rapid dissipation of the C02 vapor
D.the C02 gas is lighter than air and a large amount is required to extinguisha fire near the deck