My grandpa transplants some trees to his garden it is the best time for them every year.A

问题补充：

My grandpa transplants some trees to his garden it is the best time for them every year.

A. where

B. when

C. that

D. until

答案：

A. where

(答案→)B. when

C. that

D. until

解析： 考查状语从句。Where哪里，when当什么的时候，until直到，句意：我爷爷给他的花园移植了一些树，当每年对它们来说是最好的时节。故选B。