1 is not correct, because the line is not going across the middle of the circle.
2 is correct, radii is plural for radius. S is the center of the circle so all lines stemming from it are radii.
3 is not correct, because if ST and SQ are the same, and ST is 6cm, then SQ is 6cm and not 12cm.
4 is correct, because if SQ is 6cm then SP, the other half, is 6cm as well. Added together, PQ is 12cm.
