3的倒数是( )
A:﹣3
B:3
C:-13
D:13
—Which of the two subjects do you like, PE or music?—— . They are really interesting.
若直线x+ay+1=0与直线x+2y+3=0平行,则实数a=( )
枯草杆菌在生态系统中属于( )