We work hard to earn money. (Compound)

compound sentence এ মূলত 

But,or,and,yet ইত্যাদি বসে, আর complex sentence এ so that,unless, if,though, although, ইত্যাদি বসে।

যেহেতু বাক্যটিকে compound sentence করার জন্য বলা হয়েছে তাই উত্তর হবে অপশন 4। আর complex হলে অপশন 3। 

Here’s a breakdown of the sentences provided:

We work hard to earn money.

• Compound: No. This is a simple sentence.
• Explanation: This is a simple sentence with a clear purpose: to explain why "we work hard."

We work hard to earn a lot of money.

• Compound: No. This is also a simple sentence.
• Explanation: Similar to the first sentence, but with additional detail ("a lot of money").

We work hard so that we earn money.

• Compound: No. This is a complex sentence.
• Explanation: It contains a dependent clause ("so that we earn money") and an independent clause ("We work hard").

We work hard so that we can earn money.

• Compound: No. This is a complex sentence.
• Explanation: Similar to the third sentence but with the modal verb "can" added.

We work hard and we want to earn money.

• Compound: Yes.
• Explanation: This is a compound sentence, consisting of two independent clauses ("We work hard" and "we want to earn money") joined by the conjunction "and."

we work hard and we want to earn money is a compound sentence.