a. Some people are sitting at the tables

b. Some people are carrying meals across a room

c. Some people are placing chairs at the bar

d. Some people are waving at each other

입니다. 

a가 답인데, 사람들 전부 의자에 앉아있거나 서있는데 왜 a가 답으로 나와있나요?테이블에걸터앉을수도있는거아닌가요

명백하게보면 a도 오답인데요