Read the following story and answer the questions that follow :
The monkey and dolphin
A sailor, embarking on a voyage to Greece, took along a monkey to amuse him on shipboard. Off the coast of Greece, near Athens, a violent storm arose. Angry waves beat against the ship and dashed it to pieces. The sailor, his monkey, and all the crew jumped into the sea and swam for their lives. A dolphin saw the monkey struggling in the water and came to his assistance. The dolphin swam with the monkey on his back towards the shore. Then the dolphin, thinking the monkey was a man, asked, "Are you,sir, an Athenian?"
"Certainly I am," the monkey replied, "and furthermore I am descended from one of the noblest families of Athens."
"Then of course you know Piraeus," the dolphin said. The monkey did not know that Piraeus was the famous harbor of Athens. "Oh yes," he said, "I know Piraeus very well. He is one of my closest friends." The dolphin was so angered at these lies that he dived into the water and swam away, leaving the monkey to flounder helplessly in the sea. Then he called back to the monkey,
"Those who tell falsehoods sooner or later find themselves in deep water."
What is the meaning of ‘flounder’?
A To throw away
B To swim in sea
C To sink in sea
D To struggle helplessly