Which of the following statement(s) is/are correct about calyx?

A. Calyx is the outermost whorl of the flower and are called sepals.

B. Sepals are green, leaf like and protect the flower in the bud stage.

C. The calyx may be gamosepalous (sepals free) or polysepalous (sepals united).

D. Both (a) and (b)

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