设集合A=B=N,映射f:n→2n+n,则在映射下,象20的原象是( )
A.2
B.3
C.4
D.5
由2n+n=20求n,用代入法,
当n=4时,2n+n=20,可知选C.故选C.
Your composition should be based on ____ outline given in_____ Chinese below.
A.the, the
B.an, the
C.an, /
D.the, /