$(a)$ How many gene sets should a germ cell have?
$(b)$ Mention two factors causing evolution.

(N/A) germ cell should have one set of genes. This is because germ cells are haploid $(n)$ and are formed through meiosis,ensuring that when they fuse during fertilization,the resulting zygote has the correct diploid $(2n)$ number of chromosomes.
$(b)$ Two factors causing evolution are:
$(i)$ Genetic drift (random changes in gene frequency).
$(ii)$ Natural selection (differential survival and reproduction of individuals based on their traits).