The correct option is A Biconvex
The shape of sporangium in fern is biconvex. Each sporangium has a multicellular stalk and a biconvex capsule. A sporangium is an enclosure in which spores are formed. It can be a single cell or multicellular. Sporangia can produce asexual spores by mitosis, but in nearly all land plants and many fungi, sporangia are the site of meiosis, and produce genetically unique haploid spores. In ferns, each sporangium is a capsule, that contains spores. They are usually aggregated into clusters called as sori. The position and arrangement of the sporangia are very important for the identification of ferns. Fronds that have sporangia on their underside are fertile, and those that don't are sterile.