seen是过去分词,表示被动啊.
题目意思是：为了让别人看到自己(即“为了让自己被别人看到”),发言者爬到了椅子上.
To make himself seen (by others),...=To make others see him,...
再如：The teacher speaks loudly to (make herself heard by the students of the back row).
括号里=make the students of the back row hear her.
为了让后排的学生听到,老师说话声音很大.
希望对你有用,不懂追问!