M={(x，y)|x+y=0}，N={(x，y)|x？ +y？ =0，x∈R，y∈R}={(0，0)}

Where (0,0) ∈ m

So n is a subset of m.

Then M∪N=M, m ∪ n = n.

So choose one

2.

P={x|x=2k，k∈Z}，Q={x|x=2k+ 1，k∈Z}，M={x|x=4k+ 1，k∈Z}

a∈P，b∈Q

Then a = 2k 1 and b = 2k2+ 1.

So a+b = 2k1+2k2+1= 2 (k1+k2)+1∈ q.

So b is right.

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