What must happen before meiosis can begin? A. Four gametes must be produced.
B. The four tetrads must be pulled apart.
C. DNA doubles and produces sister chromatids.
D. The cell membrane pinches together.

Which statement best describes the relationship between observations and conclusions? a) observations are based on conclusions b) conclusions are based on observations c) observations and conclusions both depend on research d) neither conclusions nor observations depend on research.

1. which of the following transport mechanisms utilizes energy? a. osmosis b. diffusion c. facilitated diffusion d. endocytosis

Fossils of ancestors of the modern horses show a small 4-toed almost dog-like browsing animal named eohippus over time the horses got larger lost toes and changed to a grazing diet what is the best explanation of why this change occurred