问题补充：
He focused his effort the house sale for fear that the prices of them would go up suddenly.
A. on; for
B. on; in
C. to; for
D. to; in
答案：
(答案→)A. on; for
B. on; in
C. to; for
D. to; in
解析：考查固定词组。固定词组focus…on…聚焦于…；for sale出售；句意：他很注意出售的房屋的价格，唯恐房价突然上升。故A正确。
