Need help with parts c and d. please explain as well :)

Exercise 2.25 Prove that the following languages over the alphabet {a,b} are not regular: a) L = {a"banin #0} b) L = {a"b"a" |n #0} c) L = {ab"|, n 0,i=n or i = 2n} d) L = {www is any string}