Excessive air leakage into the suction side of a centrifugal pump would be indicated by which of the following operational problems?（）
A. The pump delivers full capacity when started, but gradually slackens off toan abnormally low flow
B. The pump packing gland overheats after short operating periods
C. The motor over-current protective device continually shuts the pump down
D. Pounding noises can be heard at the pump suction chest
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