题目

 It was at the very beginning____ Mr. Smith made a decision ___we should send for a doctor． A. what，thatB. that，whichC. which，thatD. that，that 答案：D10、下列有关催化剂的说法，正确的是（　　）A、二氧化锰是催化剂B、催化剂在反应前后质量不变C、催化剂都能加快反应速率D、催化剂在化学反应前后化学性质发生改变