下列关于空值的描述中，正确的是______。
A、空值等同于数值0C
暂无解析
_____theirhelp,wewouldnothavesucceeded.
Itisimperativethatstudents_____theirtermpapersontime.
There_____nothingmorefordiscussion,themeetingcametoanendhalfanearlier.
.IfyouhavereallybeenstudyingEnglishforsolong,it’sabouttimeyou_____abletowritelettersinEnglish.
At______,photographyisachemicalprocess,duringwhichalight-sensitivematerialisalteredwhenexposedtolight.
