The box was very heavy, but Tom still ( ) to carry it home.
A. manage
B. manager
C. managed
D. management
People close their windows at night in an attempt to shut( )the sound of gunfire(枪声).
A. on
B. in
C. out
D. up
You are asking ( )_ trouble if you let your child play with fire.
A. for
B. at
C. in
D. out
实数域上的二次多项式当判别式△满足()时不可约。
A. △<0
B. △>0
C. △<1
D. △=0