----Are Mr. and Mrs. Wang living alone in the house?

----Yes, altough they have three sons,      of them live with their parents.

A．neihter

B．both

C．all

D．none

果树、西瓜等经济植物，以追求品质为主，施用（）可降低果品酸度，提高甜度。

A.氮磷复混肥料

B.磷钾为主的复混肥料

C.氮磷钾三元复混肥料

D.不含氯的三元复混肥料