Final answer:
The correct sentence punctuation is a) Before we send the proposal to the customer, we must double-check all pricing information.
Step-by-step explanation:
The sentence that is correctly punctuated is:
a) Before we send the proposal to the customer, we must double-check all pricing information.
The correct use of punctuation in this sentence includes the comma before the coordinating conjunction 'we', separating the initial dependent clause from the main clause. This correctly shows the relationship between the two ideas and helps to avoid confusion or misinterpretation.