Why would natural selection not occur without genetic variations in species?

Which of these is a major trend in land plant evolution? a) the trend toward smaller size b) the trend toward a gametophyte-dominated life cycle c) the trend toward a sporophyte-dominated life cycle d) the trend toward larger gametophytes

What's the waste product of electrons and pyruvate combining in fermentation?  

10. in which phase will crossing-over occur? a. mitosis b. metaphase ii c. prophase i d. meiosis ii