I could see Dave ____ with her sister about the arrangement of the birthday party.a) was talkingb) talkc) talkingd) to talk

To fill in the blank correctly, we need to choose the option that fits both grammatically and contextually.

1. Identify the Context

   The sentence is discussing an action (talking) that Dave is doing in relation to her sister about a specific topic (the arrangement of the birthday party).

2. Analyze the Options

   • a) was talking - This is the past continuous tense, which suggests an ongoing action at a specific time in the past.
   • b) talk - This is the base form of the verb and doesn't fit grammatically in the context of the sentence.
   • c) talking - This gerund form fits well, indicating an action.
   • d) to talk - This infinitive form doesn't work in the context since it suggests purpose rather than ongoing action.

3. Determine the Best Fit

   Considering the context, the phrase suggests that Dave was engaged in the action of speaking with her sister about the party arrangements. The past continuous form "was talking" is more suitable here as it implies an ongoing action.

4. Final Answer

The correct answer is a) was talking.