Answer:
They were unaware of Perseus approaching them on the bank and his attack surprised them.
Step-by-step explanation:
The Greek mythological tale of "Perseus and the Quest for Medusa's Head" tells the tale of how Perseus had to get Medusa's head for the king of the land they had drifted to. His quest to get the monster's head was aided by the gods who pity the young demi-god.
The Gorgons are monstrous creatures with heads full of snakes and their stares can turn a man to stone. Perseus, under the guidance of divine creatures and the gods on his side, was able to swiftly cut Medusa's head while the three Gorgons were sleeping among the weeds. Then, he swiftly flew away before the two other siblings could catch him, even though they couldn't see him as he was hidden by the Cap of Darkness.
Thus, the correct answer is the first option.