A:点燃酒精灯
B:往试管中加入锌粒
C:称量氢氧化钠
D:收集氧气
已知数列{an}是等差数列,an≠0若2lga2=lga1+lga4,则a7+a8a8+a9的值是( )
—I think we should take action to protect the endangered animals.
— .