the answer is Ocell because a cell is the building block of all things
To reduce the likelihood of human error, to gather more evidence, and to make his numbers more exact.
The correct answer would be option A. Leafy gametophytes. The feature that differentiates mosses from liverworts and hornworts are the leafy gametophytes. A gametophyte is a multicellular haploid generation which is involved in the process of alternation of genes along with a diploid generation called as sporophyte.
I think A but you should double check with some one else.