What do both 00: 00 and 24: 00 mean in 24-hour time

Okay so i'm taking an online spanish course (penn foster), and in the study guide, you have to create a bunch of sentences with words you've learned so far. translating, reading, and those kinds of things are fairly easy, but when it comes to making my own sentences, my brain just kinda waltz's away. anyone got any tips?

Turn this sentence into a negative sentence using double negation: hay alguien aquí. a. nadie aquí hay b. no hay nada aquí c. nadie hay aquí d. no hay nadie aquí

Three topic of gender stereotype in essay