To solve this problem, we need to determine the correct verb tense to use in the sentence. Let's analyze the options given:
Option A:
was watching / was hearing
- The verb tense "was watching" is in the past continuous form, which indicates an ongoing action in the past.
- The verb tense "was hearing" is also in the past continuous form, indicating another ongoing action in the past.
- This option is incorrect because it uses two continuous verb tenses, which is not necessary in this context.
Option B:
watched / was hearing
- The verb tense "watched" is in the simple past form, which indicates a completed action in the past.
- The verb tense "was hearing" is in the past continuous form, indicating an ongoing action in the past.
- This option is incorrect because it combines a simple past tense with a past continuous tense, which is not appropriate in this context.
Option C:
watched / heard
- The verb tense "watched" is in the simple past form, which indicates a completed action in the past.
- The verb tense "heard" is in the simple past form, indicating another completed action in the past.
- This option is incorrect because it describes two separate completed actions in the past, but does not indicate any relationship between them.
Option D:
was watching / heard
- The verb tense "was watching" is in the past continuous form, indicating an ongoing action in the past.
- The verb tense "heard" is in the simple past form, indicating a completed action in the past.
- This option is correct because it combines an ongoing action (was watching) with a completed action (heard) in the past, which accurately describes the sequence of events.
Therefore, the correct answer is Option D:
was watching / heard
.