The __________ customer complained about everything on the menu.

The correct answer is B: querulous. This question assesses your vocabulary and ability to choose the most appropriate word based on context.

The sentence states that the customer "complained about everything on the menu." This action clearly indicates a negative and fault-finding disposition. We need a word that describes someone who is prone to complaining.

• The word querulous means complaining in a petulant or whining manner. It perfectly describes a customer who finds fault with every item and expresses dissatisfaction.
• Option A: happy is the opposite of someone who complains.
• Option C: silent means not speaking, which contradicts the act of complaining.
• Option D: satisfied is also the opposite of someone who complains about everything.

Therefore, "querulous" is the only word among the choices that accurately and effectively describes a customer who complains about everything on the menu, making it the best fit for the blank.