单项选择题
A.welding brackets across both ends of the crack
B.chipping out and slot welding the entire crack
C.drilling a hole at each end of the crack
D.cutting a square notch at each end of the crack
单项选择题 The fire extinguishing action of CO2 comes mostly from （）.
单项选择题 The amount of expansion space to be left in a fuel tank when fuel oil is being received, is determined by the （）.
单项选择题 If the overflow tank high-level alarm sounds while the fuel oil tanks are being topped off, the engineer should （）.