Diploid stages in alternation of generations life cycle

Steps:

• Define diploid as cells with two sets of chromosomes (2n), starting from zygote formation.
• Examine stage 1: Zygote results from gamete fusion (n + n = 2n).
• Examine stage 2: Haploid phase, such as gametophyte, produced by meiosis (n).
• Examine stages 3 and 4: Diploid sporophyte development and maintenance (2n via mitosis).

Why B is correct:

• Stages 1, 3, and 4 represent the 2n zygote and sporophyte phases, per the definition of diploidy in plant life cycles.

Why the others are wrong:

• A includes stage 2, a haploid gametophyte.
• C includes stage 2 (haploid) and omits diploid stages 1 and 4.
• D includes stage 2 (haploid) and omits diploid stage 3.

Final answer: B