The correct option is C Spikelet
Gramineae flower - Reproductive structures are distinct in that the inflorescences are made up of subinflorescences known as spikelets. The grass spikelet is defined by two basal sterile bracts or glumes. These subtend either a single (simple spikelet) or several (compound) florets. The term floret, when applied to grasses, refers to the flower and two fertile bracts that usually enclose the flower, the lemma and palea. The perianth is reduced to vestigial structures, lodicules, positioned beneath the ovary and the fruit is single-seeded with the testa adnate to the pericarp, a caryopsis. In contrast to most large families, the fruit is usually not needed for species identification. So, the inflorescence of Gramineae is spikelet and not raceme, spike and thyrsus.
Therefore, the correct answer is option C.