The term "bitter lesson" in the second paragraph can best be read as a

an expression designed to call something to mind without mentioning it explicitly; an indirect or passing reference.

scholarship is an sc because, by definition, a subject complement is the adjective, noun or pronoun that follows a linking verb, for example the verb be (in any of its forms).

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.