Write a program that checks if a sentence is correct according to the “English” grammar in §6.4.1. Assume that every sentence is terminated by a full stop (.) surrounded by whitespace. For example, birds fly but the fish swim . is a sentence, but birds fly but the fish swim (terminating dot missing) and birds fly but the fish swim. (no space before dot) are not. For each sentence entered, the program should simply respond “OK” or “not OK.”