Within the dna double helix, what are nucleotides together by ?

How are carbon dioxide emissions affecting the earths natural cycle of temperature change? plz apex

Twin boys have girlfriends one of the couples have a baby would the dna of the lil baby be the same as the couples dna bc the boys are identical twins

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.