Step 1

When we fold the star along this line, both sides of the star is symmetrical.

Step 2

Next, we observe the same thing when this star is folded along this line.

Step 3

Same observation here...

Step 4

..and here...

Step 5

... and finally, it is the same here as well..

Step 6

From Step 1 to Step 5, we can see that this star has 5 lines of symmetry.

Hence, the answer is C.