单选题 Container-grown plants can be planted at any time of the year, but ______ in winter.
A. should be B. would be
C. preferred D. preferably

【正确答案】 D
【答案解析】[解析] 词义辨析。
should be/would be应是；preferred首选的(adj.)；preferably更适宜，最好是 (adv.)；因此应填D。