Select the correct passive form of given sentence.

We can buy diamonds, but we cannot buy sympathy.

Diamonds can be bought but sympathy cannot be brought.

The correct passive form of the sentence "We can buy diamonds, but we cannot buy sympathy" is Diamonds can be bought but sympathy cannot be brought.

The other options are incorrect because:

• Diamonds can be bought but sympathy can be brought is incorrect because the word "brought" is in the active voice, not the passive voice.
• Diamonds cannot be bought but sympathy cannot be brought is incorrect because the word "cannot" is used twice.
• Diamonds can be bought and sympathy cannot be brought is incorrect because the word "and" is used to join two independent clauses, but the two clauses in this sentence are not independent.