题目

Imagine you choose to join WorldBook Day Book Club. Now you are reading a book on art for children. About artArt is a vast subject, including all kinds of pictures and sculptures. This book introduces 32 works by some of the world’s most famous artists. This is only a small selection, but it reveals（揭示）huge differences in what artists do. Why make art?Artists make art for many reasons. Sometimes, they just want to create something beautiful. But hundreds of years ago-when many people couldn’t read-paintings were often designed to illustrate stories. Very grand paintings were usuall在等边三角形、直角三角形、平行四边形、菱形、正方形中，一定是中心对称图形的有________个．