She had difficulty keeping her eyes open (= because she was very tired) .

她連睜開眼睛的力氣都沒有了。

He was breathing through his open mouth.

他張著嘴呼吸。

此時形容詞open反義詞： closed

再看：

He was so sleepy that he could hardly keep his eyes __________.

A. open B. opening C. opened D. to open

此題應選A。容易誤選B。主要是受 keep...doing 這一常用句式的影響。

做好本題的關鍵是要分清：open 表示“開”這一意義時，是形容詞還是動詞。

1. open用作形容詞時，表示狀態，意為“開著的”。如：

His eyes were wide open. 他的眼睛睜得大大的。

She had left the door wide open .

她把房門敞開著。

The pass is kept open all the year.

通道一年到頭暢通無阻。

The shop isn’t open today. 商店今天不開門。

He was quite open about his reasons for leaving.

他對離開的原因完全未加隱瞞。

He had always been open with her and she always felt she would know if he lied

他對她總是坦誠相待，她也一直覺得如果他說謊，自己一定能察覺。

《柯林斯高階英漢雙解學習詞典》

I&39;m a very open person.

我這個人非常坦誠直率。

2. open用作動詞時，表示動作，意為“開”。如：

She opened her arms and gave me a big hug.

她張開雙臂，緊緊地擁抱了我。

《柯林斯高階英漢雙解學習詞典》

Open your mouth and say &34;ah&34;. 張開嘴說“啊”。

Please open the window. 請打開窗戶。

What if the parachute doesn&39;t open?

降落傘打不開怎么辦？

The flowers are starting to open.

花開始綻放了。

open用作動詞，是終止性動詞，通常不能用來表示“開”這一動作的持續。如。如：

這門打開已有一周了。

正：The door has been open for a week.

誤：The door has been opened for a week.

晚上讓窗戶開著。

正：Keep the window open at night.

誤：Keep the window opening at night.

keep sb(sth) doing sth.使某人或某物不定地做某事（動作之間稍有間隔）

通過以上分析，我們可以清楚地知道：上面一題應用keep...open, 而不能用keep...opening, 其道理已很顯然。假若我們要用keep...opening, 那其實就是要使open 這一終止性動作不斷地反復發生，這顯然是荒唐可笑的。

順便說一下：

keep one’s ears/eyes open (for sth)

（對…）保持警覺；注意；留心

to be quick to notice or hear things