"Mary surprised all of us when she told us about her plan."
Here's why:
* Pronoun Case: The pronoun "us" is in the objective case because it is the object of the verb "told."
* Compound Subject or Object: The sentence includes a compound object, "all of us," which is a combination of two or more words acting as the object of the verb. In this case, "us" is part of this compound object.
Explanation:
The sentence is structured as follows:
* Subject: Mary
* Verb: surprised
* Object: all of us
* Subordinate Clause: when she told us about her plan
The pronoun "us" is the object of the verb "told" within the subordinate clause. Therefore, it needs to be in the objective case.