Give a bnf grammar for each of the languages below.

a) the set of all strings consisting of one or more lower case letters.

b) the set of all strings consisting of one or more digits with a period between each and the next. there should be no period before the first nor after the last digit.

c) the set of all strings consisting of the keyword start, followed by zero or more commands with a period after each command, followed by the keyword stop. use the non-terminal for commands, and do not give productions for it.

d) the set of all strings consisting of a left parenthesis followed by a list of one or more lower case letters separated by commas, followed by a right parenthesis. there should be no comma before the first letter nor after the last letter.