This term three of our teachers are going to to England to have advanced studies.
A:be sending
B:are sent
C:be sent
D:send
《马关条约》与《南京条约》内容上最大的不同是( )
数列an的前n项和为Sn,已知a1=1,a2=12,an+2=an+1-an,则S2013的值为 ( )
丁烷(X)燃烧的化学方程式:2X+13O2=8CO+10H2O,则丁烷的化学式为( )