分解因式x2-2x-3,结果是( )
A.(x-1)(x+3)
B.(x+1)(x-3)
C.(x-1)(x-3)
D.(x+1)(x+3)
x2-2x-3=(x+1)(x-3).
故选B.
These are my ________.[ ]
A. a computer game
B. computer game
C. computer games
对树木进行切刻,纵伤与横伤的深度应该达到______。
A.表皮层
B.真皮层
C.韧皮部
D.木质部