please specify the correct choice

1. Here is a grammar, whose variables and terminals are NOT named using the usual convention. Any of R through Z could be either a variable or terminal: it is your job to figure out which is which, and which could be the start symbol. We do have an important clue: There are no useless productions in this grammar; that is, each production is used in some derivation of some terminal string from the start symbol. Your job is to figure out which letters definitely represent variables, which definitely represent terminals, which could represent either a terminal or a nonterminal, and which could be the start symbol. Remember that the usual convention, which might imply that a) Z could be a variable or a terminal. b) Y could be a variable or a terminal. c) Vmust be a terminal. d) Vmust be a variable