Brian’s eyes felt tired because he … on his laptop for hours. Choose the correct response: Could I speak to Ken Logan, please? Jane has been learning Russian … the last two years. … the time you called me; I had already left my flat. Kate and Lisa decided … French lessons together. This time tomorrow, I … on my new computer. Why is he … his nails? Jane ... a new computer game onto her computer.

Brian’s eyes felt tired because he had been staring at his laptop for hours.

Explanation: The phrase "because he..." indicates that the reason for Brian’s tired eyes is connected to what he was doing on his laptop. In this case, the verb tense used is "had been staring," which is the past perfect continuous tense. This tense is used to describe an action that started in the past and continued until a specific point in the past. In this case, the action of staring at the laptop started in the past and continued for hours until Brian's eyes felt tired.

Step-by-step solution:
1. Identify the verb tense needed to describe the action.
2. Understand the meaning and usage of the verb tense to correctly apply it to the sentence.
3. Choose the correct verb tense form based on the subject (Brian) and the past continuous tense structure.
4. Combine the verb tense form with the rest of the sentence to form a complete and grammatically correct answer.