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题库 / Prep2007E2-DS-5
If x, y, and z are integers, is x + y + 2z even?
(1) x + z is even.
(2) y + z is even.
Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
EACH statement ALONE is sufficient.
Statements (1) and (2) TOGETHER are NOT sufficient.
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2z必为偶数，所以只要x和y同号就好，则和为偶数。这两个条件单看都不能得知xy同号，一起可以。
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