已知等差数列{an}中，a2=6，a5=15，若bn=a2n，则数列{bn}的前5项和等于[ ]
A.30
B.45
C.90
D.186
答案：C
Helen got up too late this morning, so she went to school _____ breakfast.
A．without
B．through
C．for
D．with
钢包精炼炉内吹氩效果主要有哪些？
