Alphabetic sequence with fixed middle: extend QAR, RAS, SAT, TAU, ____ by advancing the first and last letters by +1 while keeping the central 'A' unchanged.

The form is (Letter, 'A', Letter) with +1 steps on the outer letters.

• First letters: Q → R → S → T → U (+1).
• Second letters: constant 'A'.
• Third letters: R → S → T → U → V (+1).