George is constructing the circumscribed circle for △RST. He has already used his compass to complete the part of the construction shown in the figure.



Which construction could be his next step?

Construct the line through points A and T and a second line through points B and S.

Construct the line through points A and C and a second line through points B and D.

Construct the line through points A and B and a second line through points C and D.

Construct the line through points A and D and a second line through points B and C.