Which of the following statement is correct w.r.t diagram?

• A

  ‘A’ is mucilaginous sheath and is found in Rivularia.

• B

  ‘A’ is mucilaginous sheath and is found in Anabaena.

• C

  ‘A’ is heterocyst and is found in methanogens.

• D

  ‘A’ is heterocyst and is found in Nostoc.