The sentences that give examples of similes are:
-
"When Andre picked up the calculus textbook, it felt like a 600-page slab of concrete." (This uses "like" to compare its heaviness.)
-
"After the rain, the beach was as hot and humid as the inside of a pressure cooker." (This uses "as" to compare the heat and humidity.)
So the two correct answers are the first and the fifth sentences.