Explanation:

- The task is to connect two sentences about undocumented and temporary foreign workers using a suitable connector.

- The sentences are: "Too much is at stake for not only the nearly 11.3 million undocumented workers." and "It's at stake for the nearly 1.5 million temporary foreign workers."

- Option 1: "but also" - This correctly extends the initial sentiment to include a second group, creating a parallel structure.

- Option 2: "also" - This would not correctly connect both sentences as a smooth continuation.

- Option 3: "but" - This suggests a contrast rather than extending the idea.

- Option 4: "Only (A) and (B)" - It incorrectly suggests both options 1 and 2 can be used interchangeably.

- Option 5: "Only (B) and (C)" - It incorrectly suggests both options 2 and 3 can be used interchangeably.

The correct answer is:

- Option 1: but also