下列图象中,能正确描述液体凝固成晶体的图象是( )
A:
B:
C:
D:
Mr. Liu is a ____. He works in Bao'an People's Hospital. His house is ____ from the hospital. So he goes to work by ____.He is ____. He helps lots of sick people. He likes his ____.
填上>或<。
59 ____ 815
读图,回答问题。
Mum, what are you cooking? It_______ so sweet.
①不在直线系M中的点都落在面积为π的区域内
②直线系M中所有直线为一组平行线
③直线系M中所有直线均经过一个定点
④对于任意整数n(n≥3),存在正n边形,其所有边均在直线系M中的直线上
其中真命题的代号是____(写出所有真命题的代号).