What is the main reason why Venus' surface is so hot?* O The number of volcanoes on Venus
O The efficient green house effect on Venus
O The extremely fast rotation of Venus
O The great amount of water on Venus

I belive it's most likely the second one? Thats a tough one

Explanation:

couples could only have one child to reduce the population growth.

2018 means 2018 ce or common era

there have been other eras too including bce, which included way more years.