However, this generally 20 when only a single or a few nails are affected.
答案：(C) applies
apply 在此是「適用」：不過這種說法通常只適用於單一或少數指甲受影響的情況；indicates（顯示）、defines（定義）、confirms（證實）語意都不合。
答對率 28%。
apply 你大概只熟 apply for a job（申請工作）與 apply to（適用於，也用於申請）。它單獨使用時是「適用、成立」：This rule applies to everyone.（這條規則適用於所有人）／The same applies here.（這裡也一樣）。
前一句說白點會隨指甲長出去、除非再受傷否則不會回來；下一句用 If all of your nails are showing white spots… could be related to another more serious condition（若十指全是白點，可能與其他更嚴重的疾病有關）作對比。本句夾在中間、以 However 起頭，就是要限縮前面那個結論的適用範圍——所以是「這通常只在少數指甲受影響時才適用」。
apply to（適用於）、The same applies.（同理適用）、apply for a job（求職）、apply pressure（施加壓力）、an application（申請、應用）。
Many people at some point in life have white spots on their fingernails. One of the most common causes for these little white spots is a condition called leukonychia. Although the name sounds pretty serious, the condition typically 16 . And while many people think the white spots are caused by a calcium or zinc deficiency, that's generally not the case.
In reality, these spots most often develop 17 mild to moderate trauma to your nail. If you can't think of anything that would have injured your nail, consider the fact that nails grow very slowly, so the injury 18 weeks before the spots ever appeared. The spots could also be a sign of a mild infection or allergy, or a side effect of certain medications.
19 the source of the injury, these spots typically do not require any treatment and should go away as your nail grows out. And they should not return unless you suffer another injury to a nail. However, this generally 20 when only a single or a few nails are affected. If all of your nails are showing white spots, the leukonychia could be related to another more serious condition such as anemia, cardiac disease, diabetes, or kidney disease.