Its past, "have experienced" meaning they've already been through it
A descriptive quote is simply a quote that throughly describes and gives details about a subject or in this case a character.
Without more information on your assignment, my best understanding is that your teacher is looking for a quote from whatever literary piece you are reading that best describes each of the characters.
I believe the answer is D) with his cunning tricks. Beowulf and his army pretended to be asleep when Grendel came, when in fact they were awake and waited for him to come so that they can kill him.
A isn't correct because no sword could hurt Grendel.
B isn't correct because no mocking words were said.
C isn't correct because no magic was used.