Which statement describes the second line of defense?

(a) The second line of defense includes biological and chemical barriers.
(b) The skin is the major organ of the second line of defense.
(c) The second line of defense keeps most pathogens out of the body.
(d) The second line of defense is encountered by pathogens that enter the body.

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?