Aaaah I need help! asap if possible

Where do homologous chromosomes exchange genetic material through crossing over?               a.  chlorophyll    b.  centrosomes    c.  centromeres    d.  chiasma

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.

Several bird species feed in a certain species of tree. each bird species feeds in a different part of the tree. which statement is true of these bird species? a. they have adapted to different niches due to competition b. they have a carnivorous relationship with the tree species. c. they have adapted to different niches due to predation d. they have a symbiotic relationship with the tree species.