Which two characteristics do polar and dry climates have in common? O high altitude and very cold winters
O very cold winters and contrasting seasons
O contrasting seasons and very little precipitation
O very little precipitation and few, specialized plants

This is all you, but i can give you some topics that you could try. if it rained when you want to do something outdoors, it 'limits' that human activity. maybe you want to do an experiment that goes throughout the whole year and you have to have above freezing the entire year. this 'limits' your activity. i thought of those just off of the top of my head. something that gets to me that might be getting to you is you are thinking too hard about what to do. think simply, and if it is too simple, then bump it up just a little bit.

Ithink it is space that makes up 70 percent

Answerair masses develop near the equator are warm; tropical air mass

Answer decreased soil salinity;