这里选c.不是时态问题.是定语从句的考察.
词句的主语是anyone 谓语是系动词is.而.after the start of the play 是修饰anyone的定语.
修改成定语从句就是
Anyone who arrived after the start of the play is not allowed in until the interval.
去掉who这个关系代词,语法规定,主语anyone和arrive 是主动形式,就要用动词的ing形式表达.
所以是Anyone arriving after the start of the play is not allowed in until the interval.