Traveling southward from the arctic regions of canada to the tropics of panama, one passes through several biomes - tundra, coniferous forest, temperate deciduous forest, and tropical rain forest. this pattern of change in vegetation is primarily the result ofa. primary and secondary successionb. an increase in both mean annual temperature and mean annual precipitation c. an increase in the total annual hours of sunlightd. the invasion of exotic species

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.

A,b,c is the answer to the question