Choose the incorrect statement with respect to microspores or pollen grains of flowering plants. 

• A

  Vegetative cell nucleus is spherical in shape. 

• B

  Generative cell floats in the cytoplasm of vegetative cell.  

• C

  In more than 60% of angiosperms, the pollen grains are released at 2-celled stage.  

• D

  Exine is made of one of the most resistant organic materials known so far.