Mr.Smith, together with his two sons,_____Shanghai for about five months.
A：has left
B：has been away from
C：have left
D：have been away from
_______ lunch, Anna and her brother _________ like hamburgers.
吹打发霉物体时，常有粉尘飞扬，这粉尘的主要成分是（ ）
生产者、消费者和分解者构成了一个完整的生态系统。
