— Mary, let’s go to the lecture by Hawking, which is said to be very interesting.

— I’d like to, but I ________ finish the report first.

A. can                     B. may                  must                      D. shall

比例税率是指对同一课税对象，根据其数额大小，划分若干等级，按照不同等级各自的比例征税的税率。( )