Ther composing an open-ended, debatable question, the next step to developing a well-supported, logical argument is to

innocence can be defined as the lack of sin, relating it with the lack of guilt, also it can be a synonime of naivety. most people agree that sins are made out of experiences, intentionally or not, as well as you stop being naive once certain things happen to you throughout your life. so, with this explained, the chosen answers are:

when the boy saw the effects of war, he no longer viewed life as innocent.

the loss of innocence is a result of gaining experience and making mistakes.

one way to define innocence is as a lack of worldly experience or sophistication.

the answer is subjective. i personally agree with the first answer for this question.

if one isn't strictly talking about objects then the correct answer would be 'my eyes' since according to this riddle i am asleep and in order to answer/open the door i need to open my eyes first of all.

however, if one is specifically looking for an object, then the first thing i would open would be the door

hope this !