经历了多次严重自然灾害后，人们才逐渐意识到植树造林的重要性。
People didn't come to realize the importance of planting trees until they (had) experienced a number of serious natural disasters.
经历了多次严重自然灾害后，人们才逐渐意识到植树造林的重要性。
People didn't come to realize the importance of planting trees until they (had) experienced a number of serious natural disasters.
