Methyl methacrylate monomer (MMA) should NOT be used because it is **extremely flammable** and **can cause serious health problems**, including:
* Allergic reactions
* Permanent loss of the nail plate
* Permanent loss of sensation in the fingertips
* Eye, nose, and throat irritation
* Respiratory problems
* Neurological problems
MMA is also difficult to remove from nails, and can damage the nail bed.
Therefore, the answer is **d**.
Here are some additional facts about MMA:
* MMA is a synthetic liquid that is used to make artificial nails.
* It is a colorless, flammable liquid with a strong odor.
* MMA is not approved by the US Food and Drug Administration (FDA) for use in nail products.
* MMA is banned in many countries, including the United States and Canada.
If you are considering getting artificial nails, make sure to ask your nail technician what products they are using. Avoid nail salons that use MMA products.