The ability is 25 to those with leaves that are hydrophobic, or repel water—a special feature that forces the liquid to move away when the leaf is exposed to it.
答案：(C) unique
【句型】unique to 字詞搭配「……所獨有的」，表示這種能力是具有疏水性葉片植物「特有的」；curious（好奇的）、relative（相對的，relative to表相對而非「特有」）、primitive（原始的）都不合。
unique 你背的是「獨一無二的」，聽起來像在稱讚某樣東西很特別、很稀有，所以放進「這種能力是 ___ 那些葉子疏水的植物」會覺得語氣太強。unique 後面接介系詞 to 時語意會收窄成「（某群體）所特有的、只有……才有的」，是中性的描述，不帶讚美——be unique to sth 就是「為……所獨有」。
關鍵在空格後緊接的介系詞 to：The ability is ___ to those with leaves that are hydrophobic。四個選項裡能自然接 to 而且語意成立的只有 unique。內容上也吻合——前一句 However, not all plants can sneeze（然而，並非所有植物都會打噴嚏）已經先劃出範圍，本句正是在說明這個範圍：只有葉子疏水的植物才有這個能力。
curious（好奇的；奇怪的）主詞通常是人，而且 be curious about 才是常見搭配；relative 接 to 時是「相對於……而言」，講的是比較基準不是所屬範圍；primitive（原始的）是在講發展階段，與「哪些植物才有」無關。
be unique to sb／sth（為……所獨有）、a unique feature（獨特的特徵）、be relative to（相對於……）、be curious about（對……好奇）、hydrophobic（疏水的）、repel water（排斥水分）。
When a person sneezes, the droplets can spread diseases. Now research shows that plants have a somewhat 21 problem. Plant diseases can also spread through tiny water drops that jump off leaves— a plant's version of a sneeze. Scientists already knew earlier that wind and splashes of rainwater can move bacteria and other germs from leaf to leaf.
22 other possible transmission routes, researchers at Virginia Tech observed water drops on the leaves of wheat plants that were infected with leaf rust. They found that the sick plants could "sneeze" and 23 tiny water drops filled with leaf rust germs, spreading the disease to neighboring plants. The researchers noticed that small drops of water on the wheat leaves would move to combine and form a larger drop. As they were moving, the energy of the droplets in motion would be released. This energy allowed the water 24 into the air, which looked just like sneezing!
However, not all plants can sneeze. The ability is 25 to those with leaves that are hydrophobic, or repel water—a special feature that forces the liquid to move away when the leaf is exposed to it.