Final answer:
The sentence that uses capital letters correctly is: 'We are going to the McDonald Observatory where we will try to see Mars.'
Step-by-step explanation:
The sentence that uses capital letters correctly is:
We are going to the McDonald Observatory where we will try to see Mars.
In this sentence, the proper noun 'McDonald Observatory' is capitalized correctly, and the first letter of the sentence 'We' is capitalized. Additionally, the proper noun 'Mars' is capitalized correctly.
Learn more about Capitalization in English