They enjoyed fresh watermelon last fall because they watermelon seeds in the spring.
A. were planting
B. would plant
C. have planted
D. had planted
网友回答
A. were planting
B. would plant
C. have planted
(答案→)D. had planted
解析：因为他们去年在春天种下了西瓜籽所以秋天他们品尝到了新鲜的西瓜。根据句意“种西瓜”是在品尝之前，而品尝是过去的事情那么种是在过去的过去所以用过去完成时态，选D