白磷、烷基铝在空气中会自行起火，属于引火源中的（）。
A.明火
B.高温
C.雷击
D.自燃引火源
参考答案：D
(c) Calculate and comment on whether the proposed changes in receivables management will be acceptable. Assuming that only 25% of customers take the early settlement discount, what is the maximum early settlement discount that could be offered (6 marks)
操纵子包括( )。
A．一个结构基因 B．多个结构基因 C．一个启动区 D．多个启动区
