Answer:
A. Stated
Step-by-step explanation:
Central idea of a text is the main information that the text wants to pass. The central idea is stated when the text makes it clear what the topic is being talked about at the moment, so the central idea is easily identified. On the other hand, the implied central idea is when the text does not make clear which theme is addressed, making it difficult for the reader to understand which is the central idea of the text and which are the secondary ideas.
The excerpt above makes it clear that the central idea of the text is the advantageous purchase made by the United States for Alaska, even in the face of public disapproval.