第21题: [单项选择]______ we have all the materials ready, we should begin the new task at once. A. Since that B. Since now C. By now D. Now that 参考答案:D 答案解析:[解析] 考查状语从句引导词。now that意为“既然”,相当于since,引导原因状语从句,例如:Now that time is pressing,stop shilly-shallying a