Выбрать наиболее подходящий модальный глагол. Английский язык

если несложно, поставь мне "лучшее решение", кликнув по нему.

1)i`m quite certain that global warming is unavoidable. 2)the most difficult thing in the world must be all the attempts to develop heavy industry and move it ahead without causing damages to the nature. 3) however, the humankind, and scientists particularly, will overcome such bumps on their way, there is no doubt about it. ) i have always had a feeling that human is the most dangerous animal on earth. 5) in turn, damaging of natural world must be quite easy. 6) a peasant never crosses himself before it begins to thunder which means that people won't understand the real harmful impacts of their actions until they've got the awful responses from the nature, and i know i`m right. 7) discovery of new panacea or gigantic sources of alternative energy, i mean harmless energy as well, might be a wonderful thing to do.

получился более менее связанный по смыслу текст.

1. at, in

2. from, to, on

3. to, about

4. from, under

5.by, on, to 

имя 3 важных изобретений и сказать все, что вы о них