That is merely because each one is a new ordered list. Each ordered list is to begin with an "A", and you've got them as separate lists, so they rightfully begin with an "A".
To make them "A", "B", "C", etc., you'll have to combine the separate ordered lists into one, like this:
<ol type="A">
<li>Crude drug</li>
<ol type="i">
<li>Irritable colon, irritable bowel syndrome (IBS),
gastritis, and entercolitis</li>
<li>Flavoring agent, mild antimicrobial, and mild antispasmodic</li>
</ol>
</ol>
<ol type="A">
<li>Menthol
<ol type="i">
<li>Mouth wash and gargles; relief of symptoms of gastric hyperacidity</li>
<li>Preparation of menthol, menthone, and some terpenes is
used for the treatment of renal stones</li>
<li>Preparation of menthol 38%, menthone 60%, and other compounds
is used for the treatment of gall stones</li>
<li>Choleretic effect</li>
<li>Decreases the symptoms of rheumatic pain</li>
<li>Preparation of menthol and limonene reduces the progress of cancer</li>
</ol>
</li>
<li>Volatile oil of peppermint
<ol type="i">
<li>Flavoring agent</li>
<li>Carminative</li>
<li>Mild antimicrobial, antispasmodic</li>
<li>In toothpastes and powders</li>
<li>In cigarettes to mask unpleasant odor</li>
</ol>
</li>
<li>Flavones
<ol type="i">
<li>Antimicrobial, anti-diarrheal, and antispasmodic</li>
</ol>
</il>
<li>Tannins
<ol type="i">
<li>Astringent, CNS stimulant</li>
</ol>
</li>
</ol>