"cu" is a pair of letters the element we call "copper".
the letter pair "cu" is not the name of an element; it’s a chemists use to represent it
a. chemical formula
b. name
c. symbol

C. Symbol

Explanation:

The letters CU is a chemical symbol used to identify the said metal.

Elements are distinct substances that cannot be split up into simpler substances. Such substances consists of only one kind of atom. The numbers of elements know till date exceeds hundred. Every matter is a combination these various elements.

In the world of science, each of the element is symbolized by a capital letter or capital letter followed by a small letter usually derived from their Greek, Latin or English names.

For copper, it is derived from a latin word Cuprum and its symbol is Cu.

the answer is c i believe

acid rain does not usually kill trees directly. instead, it is more likely to weaken the trees by damaging their leaves, limiting the nutrients available to them, or poisoning them with toxic substances slowly released from the soil. the main atmospheric pollutants that affect trees are nitrates and sulphates.