What is the posterior opening of the digestive tract called? the anterior opening?

Hummingbirds drink nectar from flowers, while robins eat plant seeds. what does this reduce?

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.

Which step is not included in the step approach to calculating the greatest common divisor?