In Deoxyribonucleic acid, cytosine pairs with the nitrogen base is

i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.

energy and particles

both male and female gametes are produced by meiosis of the germ cells. therefore, both male and female gametes are haploid. one male and one female gamete unite during the fertilization to form the diploid zygote. in seed bearing plants, pollen grain is the male gametophyte, which produces sperm cells.