There is only one answer but what is the answer.
Is there a word box for these?
I thought it was it was the first answer
D. The coffee shop was unusual full, but today were many open tables.
A compound sentence is a sentence that has two complete sentences joined together using a comma and a conjunction. "The coffee shop was unusually full" is a complete sentence by itself. "Today [there] were many open tables" is also a complete sentence by itself. These are joined together with the conjunction "but" preceded by a comma.
