Words such as ‘similar/different and problem/solution' students organize important information in textbooks.

An Antonym is a word opposite in meaning to another word, and this definition applies mainly adjectives although some other words such as: adverbs, verbs, and even abstract nouns also have antonyms.

Antonyms enrich our vocabulary providing multiple perspectives when communicating ideas.

Now, a synonym for the word Antonym is "contrasting" or "contrastive"  

Thereby, the above statement can be completed like this:  

"Contrasting/Contrastive words such as ‘similar/different and problem/solution' help students organize important information in textbooks."

in an absolute  monarchy, the  monarchrules as an autocrat, with absolutepower  over the state and government — for example, the right to rule by decree, promulgate laws, and impose punishments. the  monarch isnominally sovereign but the electorate, through their legislature, exercise political sovereignty.

the answer to your question is,

d. when a child was born.

-mabel < 3