2.78÷1.2,商是2.3时,余数是( )
A: 2
B:20
C:0.2
D:0.02
① ____ A. cold
② ____ B. outside
③ ____ C. hot
④ ____ D. inside
数列{an}满足an+1+(-1)nan=2n-1,则{an}的前60项和为( )