Although they may never be able to 20 exactly how the planet remains so stealthily hidden, scientists are sure of one thing---there are many more even darker planets out there just waiting to be discovered!
答案：(D) tell
tell exactly how（確切查明／辨識出是如何）表示科學家或許永遠無法確切查明這顆行星如何隱身，但確信還有更多更暗的行星等待被發現；make／count／read 均不符合 tell exactly 的固定搭配語意。
本題大考中心未公布逐題答對率，以下不談數據，只談觀念。
tell 這個字，你的印象大概只有「告訴」，而且總覺得後面該接一個人（tell me、tell him），所以看到它後面直接接 exactly how 帶出來的子句會覺得怪；read 反而因為「解讀」的聯想而顯得合理。
先看空格後面接的是什麼：exactly how the planet remains so stealthily hidden（這顆行星究竟怎麼藏得這麼隱密），那是一個由 how 帶頭的間接問句。再看整句的語氣：they may never be able to ______ ...（他們也許永遠沒辦法 ______），接上前一句「研究人員並不完全確定」，講的是弄不清楚、判斷不出來。tell 除了「告訴」，還有「分辨、判斷、看得出來」的意思，而且這個用法幾乎都與 can、could、be able to 一起出現，後面接 how、whether 或 the difference 這一類東西。國中的掛鉤就是 What's the difference between A and B? 與 It's hard to tell.（很難說、很難判斷）。
make 若要表達「看出、辨認出」得走 make out 這個片語，單獨一個 make 後面接 how 子句不成立。count 是「計算、數」或「有分量、重要」（Every vote counts.），與「弄清楚原理」無關。read 雖然有「解讀」的引申義，但受詞通常是讀得到的東西或訊號（read a map、read her expression），後面直接接 how 子句不是它的用法。
can tell（分辨得出、判斷得出）、It's hard to tell.（很難判斷）、tell the difference between A and B（分辨 A 與 B 的差別）、make out（看出、辨認出）、remain hidden（保持隱藏）、Every vote counts.（每一票都算數）
Astronomers have discovered the darkest alien planet known to exist in the galaxy.
The Jupiter-sized planet, known as TrES-2b, is located in another solar system some 750 million light years away from Earth. Reflecting less than one percent of the sunlight 16 on it, TrES-2b is less reflective than black acrylic paint, and is blacker than coal. The only light that comes from TrES-2b is a faint red glow, 17 the heated coils on an electric stove or a very dim light bulb. Researchers believe this results from its extremely hot atmosphere, which is as high as 1,800°F (980°C), 18 its closeness to its sun—its source of energy.
So how does this planet manage to absorb about 99% of the light it receives from its sun? 19 researchers are not completely sure, they believe it could be because its atmosphere is composed of light-absorbing chemicals like vaporized sodium or even some elements whose existence is not yet known. Although they may never be able to 20 exactly how the planet remains so stealthily hidden, scientists are sure of one thing—there are many more even darker planets out there just waiting to be discovered!