What is the focus of this passage？
A. How firefighters carry out their responsibilities.
B. The proper installation of home smoke detectors.
C. The detoction of dead-air space on walls and ceilings.
D. How smoke detectors prevent fies in homes.
A smoke detector must always be placed______.
A. on any level of a home
B. outside all hedrooms in a home
C. in all hallways of a home
D. in kitchens where fires are most likely to star
What does "POP" probably mean？
A. Places of presence．
B. Patterns of presence．
C. Period of presence．
D. Probability of presence．
A公司的某项目即将开始，项目经理估计该项目10天即可完成，如果出现问题耽搁了也不会超过20天完成，最快6天即可完成。根据项目历时估计中的三点估算法，你认为该项目的历时为(37)，该项目历时的估算方差为(38)。
A. 10天
B. 11天
C. 12天
D. 13天
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