With great efforts he passed the examination change into compound sentence​

in the following paragraph, the fourth sentence the correct answer is: three personal subject pronouns

”she was embarrassed when she found that they had been put back on the shelves…”

a   subject pronoun is a personal pronoun. i, you, he, she it, we, they.  

in the sentence it can be observed she, used twice and they used once. is for this reason that is a three personal subject pronoun sentence.