Answer:

1. Person A: "I'm beat. I've been working like a dog all day."

Person B: "Yeah, me too. I'm ready to hit the hay."

Person C: "I hear you. I'm feeling the grind today, too."

2. Person A: "I'm so sick and tired of this weather. It's been raining cats and dogs."

Person B: "Tell me about it. It's been a real downer."

Person C: "I hope this rain stops soon. I'm starting to feel like a drowned rat."

3. Person A: "I can't believe how much work we have to do. It's like trying to find a needle in a haystack."

Person B: "Yeah, it's a real tough row to hoe."

Person C: "I know, right? But we'll power through it. We're in the same boat, after all."

Idiomatic expressions are phrases that cannot be understood based on the meanings of the individual words. They are often used to convey a more casual or informal tone in conversation.

The idiomatic expressions used above are:

"working like a dog" means to work very hard

"hit the hay" means to go to sleep

"feeling the grind" means to feel the stress of hard work

"raining cats and dogs" means raining heavily

"downer" means something depressing

"drowned rat" means someone who is wet and bedraggled

"like trying to find a needle in a haystack" means that something is very difficult to find

"tough row to hoe" means a difficult task

"power through it" means to persist and overcome

"in the same boat" means to be in a similar situation.