Arrange the following four layers of microsporangium in correct centripetal sequence as seen in the transverse section.

A. Middle layers       B. Epidermis     C. Tapetum      D. Endothecium

• A

  B, D, A and C

• B

  B, A, D and C 

• C

  B, D, C and A

• D

  B, C, D and A