What type of white blood cell is activate memory cells ?

Memory B lymphocytes. Bm lymphocytes are cells involved in the secondary innate humoral immune response. They also, like other B cells, produce antibodies after the first exposure with an antigen and then produce large amounts of antibodies shortly after another exposure to the same antigen.

Explanation:

i need

yes, because even though a theory has a  lot of evidence to support it, it is not always true