Answer :

To determine the number of spaces you should type after a period at the end of a sentence, let's break it down step-by-step:

1. A punctuation mark, such as a period, signals the end of a sentence.
2. The number of spaces that should follow a period at the end of a sentence can vary based on different writing conventions and styles.
3. Modern writing conventions, including those followed by widely accepted style guides such as the American Psychological Association (APA) and the Modern Language Association (MLA), recommend a specific number of spaces.

Based on widely accepted writing conventions:
- The modern convention is to type one space after a period at the end of a sentence.

Thus, the correct answer to the question is:
D) one