15．－Tom, you've got an A in the final English exam. Congratulations!

－Thanks. But I never thought the result would come out so fast. The papers_____when I left the teacher's office just now.

A．were marking

B．were marked

C．were being marked

D．had been marked

按份共有人出让其在共有财产中的份额时，其他共有人在同等条件下有优先购买权。( )