Final answer:
The sentences that correctly use conjunctions and punctuation are provided.
Step-by-step explanation:
The correct sentences that use conjunctions and punctuation are:
- China now has population of older adults, and one child alone has the financial burden of caring for two parents and four grandparents.
- China now has population of older adults, but one child alone has the financial burden of caring for two parents and four grandparents.
The first sentence uses the conjunction 'and' to join two independent clauses. The second sentence uses the conjunction 'but' to contrast two ideas.
Learn more about Conjunctions and punctuation