Why is the question what is an plane so difficult to answer

Look below - A plane is math related.

Explanation:

a flat surface on which a straight line joining any two points on it would wholly lie.

"the horizontal plane"

synonyms:

flat surface · level surface · the flat · horizontal

Hope this Helps!

I Don't Know what your asking but if your trying to figure out what a plane is this might help

1.  a flat surface on which a straight line joining any two points on it would wholly lie.

2. a level of existence, thought, or development.

3. completely level or flat.

4. (of a bird or an airborne object) soar without moving the wings; glide.

Also I don't know why this would be biology related.

answer; i believe the correct answer is ( proteins );

the element that provides strength to the exoskeletons of clams and oysters is phosphorus.

this is so because calcium carbonate is the main component in the shells. calcium carbonate is strengthened by phosphorus.

explanation: