Substitude the underlined word by a direct object pronoun. Il voit le professeur dans la salle de classe.

Il le voit dans la salle de classe.
Il voit le dans la salle de classe.
Il la voit dans la salle de classe.
Il voit lui dans la salle de classe.

Before i start, just letting you know, language teachers are very seriously strict about getting answers from other people, especially online. putting this question out online could be counted as cheating, and having experienced issues where teachers thought i was cheating when i wasn't, it's not fun if you get caught. so i'm going to show you how to do it, but i'm not going to do all of them for you.so the first one has no verb, so you should just be able to change the 'le' to 'les' and just add an s to the end of 'crayon'. that one's kind of easy in that way. voici les crayons.when it has a verb like in #2, you also have to change the verb. the 'c'est' would change to 'ce sont' since that's the plural form of etre. then, since it's not a le/la and it's just one eraser (gomme), it changes to 'des' indicating that there are some crayons instead of all the crayons. then, as with usual plurals, the noun adds an s on the end of it. ce sont des gommes. hopefully that you enough to let you be able to do this work without getting in trouble for them thinking you're cheating. if your teacher or other people in your class are willing to you learn how to do it without doing it for you, that's going to be a much better source of assistance than something like this online.

I already answered but thanks