One body plan, called bilateral symmetry, represents a major branch point in animal evolution and can be described as : most animals with bilateral symmetry have a "head end containing a brain. a. being a stationary indlividual b. an animad. jthat is idetical all around a central axis c. a body plan with only one way to split it into two equal halves-right down the midline d. resembling a pail

( c) A body plan with only one way to split it into two equal halves- right down the midline .

Explanation:

This is one of many characteristics of mammals . They do have a body shape that are identical along an axis or plane, or midline called sagittal plane or plane symmetry. From this question, the answer is c.,  though the internal organs may not be distributed symmetrically.

cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!