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问题 多项选择题

进度偏差对施工成本偏差分析的结果有重要影响，下列关于进度偏差的说法中正确的是（）。

A．进度偏差为负值，表示工期提前

B．进度偏差为负值，表示工期拖延

C．进度偏差为正值，表示工期提前

D．进度偏差为0时，表示进度正常

E．进度偏差为正值，表示工期拖延

答案

参考答案：A, D, E

单项选择题

关于脊髓灰质炎病毒的特性，下列哪些是正确的？（）

A.核酸为单链负股RNA

B.对紫外线、干燥敏感，在污水或粪便中可存活数月

C.感染机体后不形成二次病毒血症

D.病后免疫力不牢固，仍需服用脊髓灰质炎减毒活疫苗

E.预防接种对象主要是青壮年
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单项选择题

MIDI enables people to use (51) computers and electronic musical instruments. There are actually three components to MIDI, the communications " (52) ", the Hardware Interface and a distribution (53) called "Standard MIDI Files". In the context of the WWW, the most interesting component is the (54) Format. In principle, MIDI files contain sequences of MIDI Protocol messages. However, when MIDI Protocol (55) are stored in MIDI files, the events are also time-stamped for playback in the proper sequence. Music delivered by MIDI files is the most common use of MIDI today.

（54）是（）

A.Video

B.Faxmail

C.Graphic

D.Audio
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