Identify A, B, C and D in this figure?

A typical angiosperm anther is bilobed with each lobe having two theca, i.e., they are dithecous. Often a longitudinal groove runs lengthwise separating the theca. Let us understand the various types of tissues and their organisation in the transverse section of an anther. The bilobed nature of an anther is very distinct in the transverse section of the anther. The anther is a four-sided (tetragonal) structure consisting of four microsporangia located at the corners, two in each lobe.