Need help please. .it's urgent .about the main event. An excerpt from Sanctuary Chapter 4: The Scent of Danger

Something floating in the water caught Deer's eye, and he kicked his legs harder and swam forward, leaving his friends behind. There was a piece of plastic on the surface. It was clear and had lots of holes in it. Stuck in one of the holes was a mallard duck.
Deer used his mouth to tear the plastic. A moment later, he managed to set Duck free.
"Thank you so much," Duck said weakly. "I’ve been stuck for so long that I’m not sure I can fly."
“Why not come with us until you feel stronger?” Beaver suggested. “We're going to find fresh berries. In fact, we're nearly there.”
Duck agreed, and a few minutes later, the friends were climbing out onto the riverbank. To their delight, a large clump of bushes grew nearby. It was packed with plump blackberries!
Deer was extremely happy to see the berries, but he still couldn’t shake the feeling that danger still lingered. They carefully approached the bush and began enjoying the juicy treat. But their moment of peace was soon interrupted.
A crack, like the sound of thunder, echoed across the sky, startling all of them.
"I know that sound," Moose said, his deep voice laced with regret. "We should not be out in the open. Be safe, my friends. Our sanctuary has been breached."
Deer watched as his friends departed and made their way to safety. Their day of rest and fun was ruined.
Deer headed home through the forest, using the trees as cover. It was hard to shake the feeling of danger. Will I ever know the peace of the river again? he wondered. He knew that from then on he would have to be much more careful. His life might never be the same.

Which of the following is a main event in this chapter?

a) Duck weakly thanks Deer and the others for helping him
b) Deer kicks his legs harder to swim ahead of everyone else.
c) Something floating in the water catches Deer's eye as he swims.
d) The animals find Duck trapped in a piece of plastic garbage.

Note: (Main event is the climax action) I think the answer is a)...what do you think? please give me an opinionThank you so much.