Learn French: Ce médecin ne boit pas d'alcool. - This doctor doesn't drink alcohol.

When you completely negate a quantity in French (meaning "zero" or "not any"), the partitive articles like du, de la, or de l' change to simply de (or d' before a vowel). Because the doctor drinks zero alcohol, the usual de l'alcool shrinks down to d'alcool.

Why does de change to d' here?

Because alcool starts with a vowel. In French, when short words ending in e (like de, ne, or le) are followed by a word starting with a vowel, they drop the e and use an apostrophe. This makes the words flow together smoothly when speaking.

If the doctor was a woman, would the sentence start with cette médecin?

No, it would still be ce médecin. The word médecin is traditionally masculine, so we use the masculine word for "this" (ce) regardless of the doctor's actual gender.

What is the infinitive (dictionary form) of the verb boit?

It is boire (to drink). It is an irregular verb, meaning it doesn't follow the standard conjugation rules. For "he", "she", or "it", the correct form is boit.