Over the course of centuries, money has come in many different such as clay tablets, coins and even pebbles. However, its has always remained the same in that money is a generally accepted medium of exchange.

Sure, let's break down the question step by step:

1. Identify the missing words: The sentence has two blanks that need to be filled in to make it complete and meaningful.

2. Contextual understanding: The sentence talks about the different forms that money has taken over centuries and emphasizes that its fundamental role has remained unchanged.

3. First blank: The sentence mentions "different" and then lists examples like clay tablets, coins, and pebbles. The word that fits here should refer to the various forms or types that money has taken. A suitable word would be "forms."

4. Second blank: The sentence states that despite the different forms, the essential characteristic of money has remained the same. The word that fits here should refer to the fundamental nature or role of money. A suitable word would be "function."

5. Complete the sentence: Now, we can fill in the blanks with the identified words.

So, the completed sentence is: "Over the course of centuries, money has come in many different forms such as clay tablets, coins and even pebbles. However, its function has always remained the same in that money is a generally accepted medium of exchange."