Symmetry is a very popular subject with the SAT writers and can be an easy way to pick up a couple of marks.
For this question two marks are awarded for all three lines of symmetry drawn correctly.
One mark awarded for two diagrams completed correctly.
No marks for just one marked correctly.
Slight inaccuracies in drawing can be allowed, provided the intention is clear. A ruler should be used.
Suggested method:
This is very much a case of using the resources that you have been provided with and recognising how they can be useful.
A mirror is certainly helpful for this question. Placing it where it is thought the line of symmetry should be and looking to see if the reflection matches the drawing. When working out where the lines should go imagine that they are folded along the line and completely overlap each other. Some children will find this very tricky, especially as two of the lines of symmetry are not horizontal or vertical.
Alternatively, use tracing paper to draw the diagrams and then fold so that the two sides completely overlap. Draw the line where the fold is. Tracing paper is often provided in the test.