Complete the second sentence so that it has similar meaning to the first sentence

I. Complete the second sentence so that it has similar meaning to the first sentence.
1. America celebrated Thanksgiving Day on the fourth Thursday of November in 1864.
--> Since 1864 ......
2. Help me do homework, and I'll take you to school.
--> If......
3.Too much use of electric lights in cities may cause light pollution.
--> Light pollution may result............
4.Most people in this village had left before the volcano erupted.
--> After.................