in the sentence The old teeth of a shark are replaced by new teeth as often as every one to two weeks.

Yes.

Yes, in the sentence "The old teeth of a shark are replaced by new teeth as often as every one to two weeks," the word "shark" can be considered both a common noun and a concrete noun.

Here's why:

1. Common noun: A common noun refers to a general class or category of people, places, things, or ideas. In this case, "shark" is a common noun because it refers to a general category of marine animals, which are known for their distinct characteristics. It does not refer to any particular shark.

2. Concrete noun: A concrete noun refers to something that can be perceived by the senses (sight, hearing, touch, taste, or smell) or that has physical existence. "Shark" is a concrete noun because it represents a tangible, living creature. Sharks can be seen, heard, and touched, and they possess physical characteristics.

To determine if a noun is common or concrete, we need to understand its usage in the context of a particular sentence or phrase. In this case, "shark" acts as both a common noun and a concrete noun.