Explanation:

- Option 1: decided

- This is the correct option. It is the past tense of "decide." Since the sentence refers to an activity that happened "yesterday," past tense is required.

- Option 2: decide

- This is the present tense of "decide." It is not suitable for a past event.

- Option 3: decides

- This form is used for third person singular present tense, which doesn't fit the context of a past event.

- Option 4: deciding

- This is the present participle form of "decide" and would not apply here without an auxiliary verb like "were."