Carbon-14 dating would be useful in finding the age of

A.

a fossilized fish found in a layer of rock estimated to be between 15,000 and 25,000 years old.

B.

a fossilized spore estimated to be over 200,000 years old.

C.

a sedimentary rock with a leaf imprint of undetermined age.

D.

an index fossil known to have lived in the oceans 1 million years ago.

The correct answer is option A. "a fossilized fish found in a layer of rock estimated to be between 15,000 and 25,000 years old".

Explanation:

It is estimated that the oldest fossils that can be reliably measured using carbon-14 must be organic and have an age of around 50,000 years. Therefore, a fossilized fish found in a layer of rock estimated to be between 15,000 and 25,000 years old will fit perfectly to be dated using carbon-14. Anything older than 50,000 years old must be dated using other radiometric dating approaches.

organisms that lack symmetry are called asymmetrical and belong to phylum porifera/sponges.

organisms with specialized stinging cells belong to phylum cnidaria. stinging cells are called cnidoblast cells.

cnidarians show two morphological forms : polyp (sessile) and medusa (mobile)

filter feeding is observed in porifera members.  

alternation of generation is observed in coelenterata or cnidaria. there is alternation of asexual polyp form and sexual medusoid form. it is also referred as metagenesis.

explanation:

the universal gravitation equation. since the gravitational force is directly proportional to the mass of both interacting objects, more massive objects will attract each other with a greater gravitational force. if the mass of one of the objects is doubled, then the force of gravity between them is doubled.