According to specialists, car engines pollute the air with carbon dioxide, so we (should/must/has to) try to use other means of transportation, such as bikes.
should
15
We (don't have to/has to/must) be careful with food waste, because it can produce greenhouse gases, and because food scarcity is very high in many countries.
must
15
We (mustn't/don't have to) waste water, because water availability is a really big problem.
mustn't
15
The population (must/should) fight governments who support the idea of deforestation!
must
15
People in cities (must/should) practice recycling more in order to bring less trash to landfills!
should
15
We (must/shouldn't/mustn't) be careful when using plastic bottles and bags - reusing them is the best way to help our surface water sources!
must
15
People (must/don't have to/should) volunteer for cleanups in their community, but they are very important and they should give it a chance!
don't have to
15
We (shouldn't/should/must) encourage more people to plant trees in their communities!