Cross over is the first way genes are shuffled to give rise to genetic diversity. Cross over takes place in sexual reproduction. The normal way that cross over occurs is chromosomes line up side by side and break off pieces of themselves, then trade those pieces with each other.
If they break the pieces at the same locus in the sequence of base pairs, the result is an exchange of genes called genetic recombination and it ensures that the daughter cells produced have a different genetic makeup from the parent cell and thus diversity occurs.
The answer would be C. Energy is used through the food chain so energy always decreases. Population size would commonly decrease according to the pyramid of food chain but since there's no answer for that, C would be the most suitable
3. Environment
The simplest definition of an ecosystem is that it is a community or group of living organisms that live in and interact with each other in a specific environment.