Which of the following statements are true: (a) If a number is divisible by 3, it must be divisible by 9. (b) If a number is divisible by 9, it must be divisible by 3. (c) If a number is divisible by 18, it must be divisible by both 3 and 6. (d) If a number is divisible by 9 and 10 both, then it must be divisible by 90. (e) If two numbers are co-primes, at least one of them must be prime. (f) All numbers which are divisible by 4 must also by divisible by 8. (g) All numbers which are divisible by 8 must also by divisible by 4. (h) If a number is exactly divides two numbers separately, it must exactly divide their sum. (i) If a number is exactly divides the sum of two numbers, it must exactly divide the two numbers separately.