Solution

Pits are discontinuities in the secondary cell wall. There are two main types of pits – simple and bordered. All pits have two essential components – the pit cavity and the pit membrane. In the simple pit, the cavity is nearly constant in width. In the bordered pit, the cavity narrows towards the cell lumen; typically, the membrane is arched over by the secondary cell wall. The pit membrane consists of the primary wall and middle lamella. As a rule, pits in the walls of adjoining cells appear in pairs called pit pairs, and the common membrane is therefore composed of two primary walls and middle lamella.
So, the correct answer is option D.