【单选题】
A <{p}>该气体中一定含有C<{sub}>2<{/sub}>H<{sub}>2<{/sub}><{br/}><{/p}>
B <{p}>该气体中一定没有CH<{sub}>4<{/sub}><{br/}><{/p}>
C <{p}>该气体中可能含有C<{sub}>2<{/sub}>H<{sub}>2<{/sub}><{br/}><{/p}>
D <{p}>该气体不可能同时含有CH<{sub}>4<{/sub}>、C<{sub}>2<{/sub}>H<{sub}>2<{/sub}>、C<{sub}>2<{/sub}>H<{sub}>4<{/sub}><{br/}><{/p}>
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