在等差数列{an}中，若a2＋a4＋a6＋a8＋a10＝80，则a7－a8的值为________；
8
Maybe you should _____________.
[ ]
A. call on him
B. call up him
C. call him up
D. make a telephone call with him
血小板致密颗粒中不含有（）。
A.ADP
B.PF4
C.5-HT
D.钙离子
E.抗纤溶酶
