In a collection of 30 dissimilar birds, 15 eat worms, 18 eat fruit, and 12 eat seeds. Accurately 8 eat worms and seeds, 8 eat worms and fruit, 7 eat fruit and seeds, and 4 eat each three types. Two birds are selected at random. What is the probability that
(a) both birds eat at least one of these food groups?
(b) both eat at least one common food group?
(c) both eat all three food types?