题目

We        in the same school for three years.    A. were studying      B. have studied       C. will study          D. study 答案：B为了让灯泡通电发热时，消耗灯泡内的氧气，达到保护钨丝的目的，通常在白炽灯泡里的玻璃柱上涂有一层红色物质，该物质是（ ）A．红磷B．氧化汞C．二氧化锰D．氯酸钾