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设集合M={a,b,c},N={0,1},映射f:M→N满足f(a)+f(b)=f(c),则映射f:M→N的个数为
A.1
B.2
C.3
D.4
设M={a,b},则满足M∪N{a,b,c}的非空集合N的个数为______________.