Chemical weathering

a. is caused by freezing and thawing
b. breaks apart rocks by physical processes
c. occurs when chemical reactions dissolve or change the minerals in rocks
d. none of above

A is physical
B is also obviously physical
C is chemical because minerals are (Dissolved)
D makes no sense 

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.

El nino is a weather phenomenon caused when warm water from the western pacific ocean flows eastward. part1baan average of 7.7 hurricanes and 3.6 major hurricanes compares to 5 hurricanes and 1.5 major hurricanes from 1995-2005