【判断题】投影运算之后不仅取消了原关系中的某些列,而且可能会取消某些元组。
【简答题】截面为矩形的非合金钢,除轧制外未经进一步加工,钢材的宽度为100mm,厚度为5mm,冷成形笔直状报验
【单选题】使用力的平行四边形法则、三角形法则、多边形法则的前提条件是( )
【单选题】In previous times, when fresh meat was inadequate, pigeons were kept by many households as a source of food.
【单选题】She ( ) go to college.No one can stop her.
【单选题】在linux系统中,指定在今天下午 5:30 执行/tmp/test.sh文件,假设现在时间是 2008年9月30日中午12:30,下面()命令是错误的。
A.
at -f /tmp/test.sh 17:30 09/30/2008
B.
at -f /tmp/test.sh 5:30pm 09/30/2008
C.
at -f /tmp/test.sh now +5 minutes
D.
at -f /tmp/test.sh +5 minutes
【单选题】Taiwan lies ______ the southern coast of China, and it’s really _____ island. Is that so
【单选题】Taiwan island lies in the _____ of China, Japan lies to the _____ of China.
【单选题】由于岩石的抗压强度远大于它的抗拉强度,所以岩石属于( )
【单选题】Taiwan lies ______ the east of Fujian , ______ the southeast of China .