You didn't underline anything. However, I can see that there are two prepositions in this sentence, and those are the words <em>into </em>and <em>of, </em>which means those are definitely underlined here.
An object of a preposition refers to words which follow a particular preposition. So, having this in mind, the word that follows into is crowd, and the word that follows of is soldiers. The correct answer is crowd; soldiers.
The correct answer is Very young owls grow slowly.
Here, the adverb is <em>very </em>and the adjective is <em>young, </em>so the adverb is used to modify the adjective, or to show a particular degree of the adjective (how young? very young.).
In the rest of the options, there is only one adverb <em>slowly, </em>and it's not modifying an adjective, but rather the verb.
