Mendel’s pea plants had either purple or white flowers. this means that the plants
can self-pollinate.
have two recessive traits.
have two alleles for the gene.
have two copies of a gene from one parent.

The correct answer is "have two alleles for the gene".

Alleles are referred to as two or more alternative forms of the gene located at the same loci in homologous chromosomes.

They code for contrasting characteristic or phenotype.

For example, tall and dwarf, green and yellow pea color, round and wrinkled pea shape etc.

Similarly, white and purple color or flowers is also a type of contrasting trait controlled by two alleles of the gene.

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.