50. 關於尿液濃縮的亨利氏祥對流交換機制(Countercurrent mechanism)下列敘述何者正確? (A)下行支管腔對水通透性低,但可主動將運出管腔 (B)上行支管腔對水通透性低,但可主動將運出管腔 (C)下行支管管腔對水通透性高,溶質主動運入管腔以增加滲透壓 (D)上行支管管腔對水通透性高,溶質被動流入管腔