Need help ASAP. thought it was C but i got it wrong. Which of the following is a result of geological changes that impact the dynamics of an ecosystem?

Humans introducing an invasive species, resulting in loss of biodiversity
Speciation, causing an increase or decrease in competition among different species
Habitat fragmentation, due to the construction of new housing complexes
Pollution from factories, causing increasing atmospheric carbon dioxide

Assume that you are interested in separating short (200-400 bp) dna molecules from a pool of longer molecules in the 10,000-20,000 nucleotide range. you have two recipes for making your polyacrylamide gels: one recipe uses 1.5 percent agarose and would be considered a “hard gel,” while the other uses 0.5 percent agarose and would be considered a loose gel. which gel should you use to separate the short (200-400 bp) dna molecules from a pool of longer molecules in the 10,000-20,000 nucleotide range?