spring is the best season-------(plant trees)为什么要加to

spring is the best season-------(plant trees)为什么要加to
spring is the best season-------(plant trees)
为什么要加to

spring is the best season-------(plant trees)为什么要加to
Spring is the best season (to plant trees).
不定式做定语.春天是最好种树【的季节】.