下列4个函数中,不能作为X的分布函数的是( ).
A、<img src="https://static.tiw.cn//s/tiw/p3/UpLoadImage/2013-05-07/872dada0-1548-48d0-82ff-55a32eaf4fb5.png" width="216" height="92">
B、<img src="https://static.tiw.cn//s/tiw/p3/UpLoadImage/2013-05-07/e2b2b49e-0c96-4d2c-b6d9-91449a864478.png" width="226" height="61">
C、<img src="https://static.tiw.cn//s/tiw/p3/UpLoadImage/2013-05-07/2d80a87b-d2ed-4752-bf29-9d50399d5cce.png" width="222" height="66">
D、<img src="https://static.tiw.cn//s/tiw/p3/UpLoadImage/2013-05-07/890ac221-35bb-49da-9f15-55fb0ab2dc26.jpg" width="212" height="49">
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