A (blank)
is a single cell surrounded
by a protective shield.

yes it is weird but true

in the year 2850, humans successfully colonized mars. the martian modules that were constructed could hold only a small population of people. it is now a century later, and the population on mars has grown to 600 people. of the current mars population, 45 people express the recessive phenotype for phenylketon- uria (pku) syndrome (pp genotype).

explanation:

the answer is c. altitude. hope this ! #brainiac