the promotor demonstrates that the quality of rice cooker is excellent.
the promotor demonstrates the quality of rice cooker that is excellent 你这句中比较容易产生歧义:1.that is excellent修饰cooker,2.that is excellent修饰quality. In addition,"that be adj."是ETS最不推荐的修饰方式之一。
the promotor demonstrates that the rice cooker is of excellent quality 这句话没错