in gerenal, the amount that a student spends for housing should

In gerenal, the amount that a student spends for housing should be held to one-fifth of the total_____for living expenses.
A. acceptance B.available C. advisable D.valuable
选B怎么解释啊？这句话的意思是什么？谢谢

in common,in the same in the field 还是in the fields? in the sky or in the air?? The girl in the hat? The world in the future the ghost in the park the wind in the willows working in the sky dying in the sun walk in the sun