The correct option that combines the two sentences using a coordinating conjunction is:
"The girl learned English at a young age, but she struggles writing essays."
This option uses the coordinating conjunction "but" to connect the two sentences.
Coordinating conjunctions are used to join two independent clauses (complete sentences) together. In this case, the first independent clause is "The girl learned English at a young age," and the second independent clause is "She struggles writing essays."
The coordinating conjunction "but" is used to show a contrast between the two ideas. It indicates that despite the girl learning English at a young age, she still struggles with writing essays.
By using the coordinating conjunction "but," the two sentences are effectively combined into one sentence, providing a clear and concise expression of the contrast between the girl's ability to learn English and her difficulty with writing essays.