12. In guard cells, _ is the dominant osmoticum in the morning, and _ is the dominant osmoticum in the afternoon.
(A) Cl-； sucrose.
(B) malate； K+.
(C) K+； malate.
(D) sucrose； K+.
(E) K+； sucrose.

1. 題目解析本題主要考察植物的氣孔調...