The correct option is C Sieve elements
Companion cells are specialised parenchymatous cells, which are closely associated with sieve tube elements. They help in maintaining the pressure gradient in the sieve tubes.
Trichomes are epidermal outgrowths present on the stem and help in preventing water loss.
Each stoma is composed of two bean-shaped (in dicots) or dumb-bell shaped (in monocots) cells known as guard cells. They possess chloroplasts and help regulate the opening and closing of stomata.
Vessels are dead long cylindrical tube-like structure made up of many cells called vessel members, each with lignified walls and a large central cavity. In plants, tracheids and vessels are the main water transporting elements.