Scientists rely on models to represent concepts and processes in physical science. which one of the following is a reason why scientists use models?
a. models are always colorful.
b. models only show large objects.
c. models might be hazardous (not safe).
d. models can represent things that are too small to see.

D. Models can represent things that are too small to see.  Scientists rely on models to represent concepts and processes in physical science because models can represent things that are too small to see. In fact, they are actually used to give a better perspective of what is occurring on these hidden to the naked eye matters –which may include atoms, cells, and entities unseen and latent. It gives scientists the ideas and structure, restructure, integrate and ponder on new hypothesis on these matters.  

The changes to agriculture in the united states since 1900 is that increased mechanization has increased food production, thereby increasing the need for labor. there has been an increased need for higher speeds of food production due the fact that the population in the united states continues to rise.