Использовать Present Continuous можно только для перевода последнего предложения - 4.Кто стучит в дверь ? Who is knocking on the door?
В остальных предложениях можно использовать только Present Simple/Indefinite, так как в этих предложениях есть слово "часто"- слово-подсказка для PRESENT SIMPLE/Indefinite? соответственно перевести нужно так:
1.Она часто плачет. She often cries.
2.Почему она часто плачет? Why does she often cry?
3.Я его не понимаю. I don't understand him. (глагол "understand" никогда не используется в Present Continuous!)
If five years ago I was asked about how I think the city of the future, then certainly I would say that this city, where instead of buses, trams and trolley buses carrying passengers spaceships and people run the factories, mills, a fully automated and subordinate to computer programs. The children in this town do not know no worries: at their disposal the best toys, rides, computer games ...
But the years pass, we get older and realize that children's dreams - it's just fantasy.
The city of my dreams - a modern metropolis with a lively, neat, comfortable houses in which there is heat and electricity, in which no water and sewer breaks, forming a fetid rivers and lakes, which are working elevators, and entrances are like showrooms.
Nowhere was the effect more felt than in the suburb