The Alexander String Quartet returns with the penultimate program in the group’s three-year traversal of the complete string quartets of Beethoven on Sunday in the Vanderhoef Studio Theatre at the Mondavi Center. At 2 p.m., the quartet will perform Beethoven’s String Quartet in C-sharp Minor, Op. 131, joined by noted lecturer, author and composer Robert Greenberg. At 7 p.m., the Alexander String Quartet will perform the same Beethoven quartet, plus the Mozart String Quartet in G Major, K. 387, with a post-performance question-and-answer session with the members of the quartet, rather than a lecture by Greenberg. Tickets are $45 general, $22.50 students and children, available at http://www.mondaviarts.org or (530) 754-2787. The 2 p.m. performance is sold out, but typically a few turned-back tickets materialize at the box office 30 minutes prior to the performance. There are still a few seats for the 7 p.m. performance. The popular Beethoven series will conclude with two more performances on June 5.