Select the formulas of simple substances from the list: Al2O3, Pb (NO3) 2, Cu, CaC2

Simple substances are those substances that are formed by the atoms of one chemical element. For example, H2 is a diatomic hydrogen molecule, O3 is an ozone molecule, Mg is magnesium. Complex substances are chemical compounds that are formed by atoms of different elements connected to each other. For example, H2O is a water molecule consisting of 2 hydrogen atoms and 1 oxygen atom.
In this list, the simple substance is Cu (copper). The rest (aluminum oxide, lead nitrate, calcium carbide) are complex.

One of the components of a person's success in our time is receiving modern high-quality education, mastering the knowledge, skills and abilities necessary for life in society. A person today needs to study almost all his life, mastering everything new and new, acquiring the necessary professional qualities.