A cow is tied to a corner (vertex) of a regular hexagonal fenced area of side a metres by a rope of length 5a/2 metres in a grass field. (The cow cannot graze inside the fenced area.) What is the maximum possible area of the grass field to which the cow has access to graze ?

A. `5 pi a^(2)`

B. `(5)/(2)pia^(2)`

C. `6 pi a^(2)`

D. `3pia^(2)`