The given expression represents the subtraction of two fractions. To subtract fractions, we need to have a common denominator. In this case, the common denominator is 45 (the least common multiple of 5 and 9). By converting 1/5 and 1/9 to have a denominator of 45, we get 9/45 and 5/45 respectively. Subtracting these fractions gives us 4/45. Therefore, the correct answer is 4/45.