在构成生物圈的各种生态系统中，动植物种类繁多且有“绿色水库”之称的是______；具有净化水源、蓄洪抗旱并以沼泽为典型的是______；属于人工的生态系统的是______和______．这些生态系统彼此密切联系，所以说，生物圈是一个______．

--Mary, where’s Simon? I haven’t seen him for days.

--He __________ Japan. This may be the third time he _________ there.

A．has been to, has gone to

B．has been to, has gone

C．has gone to, has been to

D．has gone to, has been