如果是用这个来提问 What is your favorite subject?
那么回答就是 My favorite subject is science. （这里最喜欢的科目只能说一个.）
如果提问是 What are your favorite subjects?
那么回答就是 My favorite subjects are science and English.
如果你硬要用第一问的提问,还想说两个学科的话,那么就是
What is your favorite subject?
My favorite subjects are science and English.
希望对你有帮助～