Not only his parents but also his brother           to the Summer Palace. They will be back next week.

A．have been

B．have gone

C．has gone

D．has been

周围免疫器官包括（）

A．胸腺、脾、黏膜组织

B．腔上囊、脾、扁桃体

C．骨髓、淋巴结、脾

D．脾、淋巴结、黏膜相关淋巴组织

E．扁桃体、骨髓、淋巴结