用指示代词those these that 各造一个陈述句然后变成否定句

Those are beautiful flowers.那些是美丽的花.
Those are not beautiful flowers.那些不是美丽的花.
These are Tom's toys.这些是汤姆的玩具.
These are not Tom's toys.这些不是汤姆的玩具.
That is a letter from Mary.那是玛丽的来信.
That is not a letter from Mary.那不是玛丽的来信.
注意上面的not都可以和前面的be动词缩合,缩合后分别为aren't,isn't,缩合词口语化,而不缩合则比较正式和书面化.
希望能有所帮助!Best wishes!

Those men are ugly.
These man is ugly.
That man is ugly.
Those men aren`t ugly.
These man isn`t ugly.
That man isn`t ugly.