Question

Which sentence correctly uses a comma to separate the introductory phrase? Before researchers are granted access to the rare-book stacks, they must be approved through a security screening process. Before, researchers are granted access to the rare-book stacks they must be approved through a security screening process. Before researchers are granted access, to the rare-book stacks they must be approved through a security screening process. Before researchers are granted access to the rare-book stacks they must be approved through, a security screening process.

Answer 1

The sentence that correctly uses a comma to separate the introductory phrase is the first one - Before researchers are granted access to the rare-book stacks, they must be approved through a security screening process.

Answer 2

sentence which uses a comma to separate the introductory phrase appropriately is :

Before researchers are granted access to the rare-book stacks, they must be approved through a security screening process.

Commas are frequently used punctuation in a sentence, hence they are used to create a short pause in a sentence.  They help in creating logical groupings.

When starting with the dependent clause, the sentence is punctuated after the dependent clause. In the above sentence dependent clause is  "Before researchers are granted access to the rare-book stacks" hence, comma is placed after the dependent clause and before the independent clause "they must be approved through a security screening process."