If the coolant temperature of a closed cooling water system for a diesel enginegradually increases, the trouble usually is( ).
A.a broken shaft on the freshwater pump
B.an excessive accumulation of scale in the heat exchanger
C.an incorrect thermostatic element operating range
D.lube oil in the cooling water
正确答案：B解析：gradually：逐渐地;accumulation：累积;scale：结垢;thermostatic：恒温的;range：范围译文：如果一个柴油机内的闭式冷却系统内的冷却介质温度逐渐升高，则通常的原因是热交换器内有过多的积垢。
