问题
单项选择题
If r and s are integers and rs+r is odd, which of the following must be even ？（）
A.r
B.s
C.r+s
D.rs-r
E.r2+s
答案
参考答案：B
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If r and s are integers and rs+r is odd, which of the following must be even ？（）
A.r
B.s
C.r+s
D.rs-r
E.r2+s
参考答案：B