The esophagus is a tube in which food is pushed from the mouth to the stomach. As the food is pushed through the esophagus, it becomes more compact. This is — A.
a chemical change, only.

B.
a physical change, only.

C.
both a chemical and a physical change.

D.
neither a chemical nor physical change.

Which of these statements best describes the st. lawrence seaway? the st. lawrence seaway connects the st. lawrence river with the arctic ocean. the st. lawrence seaway provides an important trading route between the u.s. and mexico. the st. lawrence seaway provides an important trading route for the u.s, but has little value for canada. the st. lawrence seaway connects the great lakes, the st. lawrence river, and the atlantic ocean.

In natural selection, what is actually “selected? ” a) alleles are directly selected b) genotypes are directly selected c) phenotypes are directly selected d) entire populations are directly selected

In what for do plants utilize nitrogen? why do they need nitrogen?