Which part of the water do lancelets inhabit?

Lower bottom part

Lancelets are aquatic animals which are slender in shape and they look like fish without eyes. They have body that is tapered at both sides. These animals feed upon the debris suspended from the entire aquatic  environment. They remain partially buried in the water bed. They use hair like tentacles to grab food from debris. These animals lives in lower bottom part of water.

looks like the answer is     c     to me!

not necessarily. higher fitness requires the organism to be reproductive successful. for example, an organism at age 10 with 15 offspring is much more fit than an organism at age 15 with only 5 offspring.