Complete the sentence: In preparation for your birthday dinner, I will help _________ the dinnerware on the table.

The correct answer is "set," and it fits perfectly in the context of preparing for a birthday dinner. The verb "set" means to place or arrange items in a specific way. When referring to dinnerware, one typically "sets" the table, which involves arranging plates, utensils, glasses, and other items needed for the meal. This action is an essential part of dinner preparation, making "set" the appropriate choice for conveying the intended meaning of arranging dinnerware.

The other options do not fit the context. "Sit" implies a position or action of resting, which does not relate to preparing dinnerware. "Sat" is the past tense of "sit," and does not indicate the action required for preparing the table. "Seat" generally refers to a place to sit or the act of seating someone, which is also not relevant in this context of arranging dinnerware.