1.Thry are going to have breakfast. 2.They are having lunch. 3.They must have tea . 4.They had dinner 为什么前面这两句加了are,后面不加are, 难道是因为前面两句是 将来时 和现在进行时加are,后面两句是一般现在时和一般过去式不加are?还有 They are eat lunch对么 和第三句一样是一般现在时,难道Must 前面不能加are么?谢谢啊