**Concept: The question tests on the ability to solve a Age Problem**

**Solution:**

Since we do not have the relation between present present ages, we use 2 variables.

Let age of the younger sister = Y and that of the elder = E

If 1 added to the age of the elder sister, then the ratio of the ages of two sisters becomes 0.5:1.

So Y/E+1=0.5/1=1/2

We get 2Y = E + 1 or

E = 2Y - 1 ... (1)

If 2 is subtracted from the age of the younger one, the ratio becomes 1:3

So Y−2/E=1/3

3Y - 6 = E ... (2)

Equating (1) and (2)

2Y - 1 = 3Y - 6

Y = 6 - 1 = 5**Option D**