1. A central angle is an angle with endpoints located on a circle's circumference and vertex located at the circle's center. A central angle in a circle determines an arc.
2. An inscribed angle is an angle formed by three points on the circle's circumference.
Angle at the Center Theorem: An inscribed angle is half of the central angle (if they determine the same arc).
In your case angles:
1. ∠QSR is insribed (determines the arc QR);
2. ∠QTR is central (determines the arc QR).
Then by Angle at the Center Theorem, m∠QTR=2m∠QSR=2·52°=104°. Arc QR has the same measure as central angle QSR.
Answer: correct choice is C.