等差数列{an}共有2m项,其中奇数项之和为90,偶数项之和为72,且a2m-a1=-33,则该数列的公差为[ ]
A.-1
B.-2
C.-3
D.3
答案:C
.Your son has kept _________ for two hours. You’d better ask him to have a rest.
A.study
B.studied
C.to study
D. studying
下列易发生中暑的情况有()。
A.出汗很少
B.长时间处于高温环境中工作
C.阳光直接照射头部引起头痛
D.身体散热困难