How are the segments of a crayfish different from those of an earthworm?

crayfish have experienced something called tagmosis where some of the segments have merged, thus they have heteronomous metamerism. the difference of the earthworms and crayfish is that earthworms have somewhat called homonomous metamerism - each of the segments looks like every other segment. 

scientists have discovered that hiv does not cause aids by the virus's direct effect on the host's immune cells, but rather through the cells' lethal influence on one another. researchers from the gladstone institutes have revealed that hiv does not cause aids by the virus's

the correct answer is 2 and 4