bio-reproduction

(1) the process of meiosis may cause crossing-over (during metaphase) which will exchange the genes bewteen the alleles. Therefore, vairation will occur.
(2) & (3) fertilization. different gametes contain different genetic information. the fusion of two gametes could have lots of probability to give different genotype. so there have vairation.

(1)formation of gametes involves meiosis, of which the mother cell is diveded into 4 daughter cells, each carries different sets of genes, u better check up your bio book, which has some pictures to show the process more clearly
(2)when the male gametes fuse with the female gametes, of course the variation of genes is doubled, since the two gametes have undergone meiosis
(3)in the above case the gametes come from the same plant, but this time the two gametes come from two plants, so the genes carried in the gametes are more variated

Because they are talking about reproduction in flowering plants.