With the sun's final habitable zone dangerously close to the star, what will a dwarf planet like Ceres need to balance?
a. being far enough from Pluto to avoid collision while
keeping behind it to avoid the sun's rays
b. being far enough from the sun to maintain its own gravity
while not getting too cold
c. being close enough to take in the sun's heat without
being sucked in by its gravity
b. being large enough to maintain organisms without
creating dangerous bacteria

Which is an advantage of having memory cells when a pathogen is encountered for a second time. a) the memory cells are what proliferate into clones of cells in response to the binding of an antigen. b) memory cells are vital to the primary immune response in that they immediately recognize pathogens even at the first encounter. c) memory cells are essentially effector cells that are short lived and attack antigens even without having a receptor specific to that antigen. d) it ensures that more lymphocytes with a receptor specific to a particular antigen will be present than in a host that had never encountered that pathogen.