Scientists who argue that modern humans evolved from a single population believe that humans came from the continent of
a. africa.
b. europe.
c. south america.
d. asia.

Scientists generally agree that the origin of modern humans was in Africa - specifically in East Africa. From there they travelled to Europe and Asia via what is today Palestine and Israel. From Asia they reached Australia and North America and from the North America they reached South America - so the correct answer is a)

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.