Seven people, A, B, C, D, S, T, and U are sitting in a row, facing north.  No one sits to the right of D. Only three people sit between D and S. Only two people sit between S and T. C sits third to the left of U. A sits to the immediate right of U. How many people sit between B and T?​​​

Given: 

Seven people, A, B, C, D, S, T, and U are sitting in a row, facing north. 

No one sits to the right of D.

Only three people sit between D and S.

Only two people sit between S and T.

C sits third to the left of U.

A sits to the immediate right of U.

Three people sit between B and T.

Thus, correct option is (b).