They E us.

The sentence describes an action performed by 'They' towards 'us'. The options are 'go', 'goes', 'went', 'was watching', and 'were watching'. Given the context of the excursion and the plural subject 'They', the past continuous tense 'were watching' fits best to describe an ongoing action during the excursion.

1. Determine the verb tense and form: past continuous for a plural subject and ongoing action.

2. Evaluate the options: 'go', 'goes', 'went' (simple past/present), 'was watching' (past continuous, singular), 'were watching' (past continuous, plural).

3. Select the correct form: 'were watching'.

were watching