The farmer didn’t know .
A. where he can plant the young apple tree
B. where can he plant the young apple tree
C. where could he plant the young apple tree
D. where he could plant the young apple tree
网友回答
A. where he can plant the young apple tree
B. where can he plant the young apple tree
C. where could he plant the young apple tree
(答案→)D. where he could plant the young apple tree
解析：英语宾语从句中一般为陈述语序。句意：这个农民不知道……。结合语境可知从句描述的是过去某时发生的动作，故助动词用一般过去时态。故选D。