My mother ______ a nurse.( )
A:am
B:is
C:are
With these words, Tom went on ________ his homework.
甲、乙二人在相同条件下各射靶10次,每次射靶成绩如图所示,经计算得:=1,S =1.2,S =5.8,则下列结论中不正确的是( )
①.a2>b2 ②.ac>bc ③.ac2>bc2 ④.a﹣c>b﹣c.