Read the sentence from the introduction [paragraphs 1-7]. Unfortunately, there are no effective treatments for most patients with smell and taste disorders. Additionally, many patients find it impossible to even be properly diagnosed. People with smelling and tasting handicaps rarely receive enough support to help with their quality of life.
Which paragraph from the section "Mirrors can change smells" helps explain what word "effective" is referring to?

A mirror will not alter a smell.

It is true, however, that mirror image molecules can have very different smells. Mirror image molecules are called stereoisomers, but they are not exact copies (think of the relationship between your right and left hands).

Two stereoisomers that with very different aromas are L-carvone and D-carvone. L'carvone smells like spearmint, and D-carvone smells like the spice cumin.

There is much more to learn and discover about the biology and chemistry of taste and smell. Those of us who study the chemical senses hope that our research will lead to tastier and healthier food, reduce the spread of insect-borne disease, improve the lives of people with smell or taste disorders and create a better understanding of the importance of smell and taste.