Although the name sounds pretty serious, the condition typically 16 .
答案：(A) isn't
本句是省略句，isn't 後面省略了與前面重複的 serious：儘管名稱聽起來嚇人，這個症狀通常並不嚴重；doesn't、couldn't、wouldn't 都無法承接 be 動詞的省略。
空格後面直接是句號，你會覺得句子沒寫完，因而不敢下手。其實這是省略：Although the name sounds pretty serious, the condition typically isn't (serious).——形容詞 serious 前面才剛出現過，第二次就省略掉，只留下否定的助動詞。
關鍵在先確認省略掉的是什麼，再決定該用哪一種助動詞。往前找，前半句 sounds pretty serious 的 serious 是形容詞，後半要否定的正是它。形容詞前面要配的是 be 動詞，所以只能用 isn't；doesn't、couldn't、wouldn't 後面該接原形動詞，接不上一個形容詞。這個順序可以固定下來：看到句尾只剩一個助動詞，先回頭找它省略掉的是什麼詞類，是形容詞或名詞就用 be，是一般動詞就用 do，有情態意味才用 can／will 那一類。驗算法：把省略的字補回去唸一遍——the condition typically isn't serious（這個症狀通常並不嚴重），再對照前半的 Although the name sounds pretty serious（雖然名稱聽起來很嚴重），讓步關係成立，方向就對了。這種省略你國中就用過，只是當時出現在簡答裡：Are you tired?—Yes, I am (tired). ／ Do you like it?—Yes, I do (like it).be 動詞的問句用 be 回答，一般動詞的問句用 do 回答。本題只是把同一條規則放進一個敘述句的後半。
doesn't 要接原形動詞，寫成 the condition doesn't 等於省略了一個一般動詞，但前半句可省略的只有形容詞 serious，沒有一般動詞可承接。couldn't 與 wouldn't 除了同樣接原形動詞之外，還多帶了「不可能」與「不會」的推測語氣，而本句 typically（通常）講的是實際情況，不是推測。
Although…, …isn't.（省略重複的形容詞）、sound + 形容詞（聽起來…）、that's not the case（並非如此）、typically（通常）、deficiency（缺乏症）。
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.