They couldn't climb up...

[fire fly]

[FONT=&quot]Hi, great people!
Could anyone help me with this question?
They couldn’t climb up the mountain because of the storm.
A. The storm made it not capable of climbing up the mountain.
B. Their climbing up the mountain was unable due to the storm.
C. The storm made them impossible to climb up the mountain.
D. The storm discouraged them from climbing up the mountain.

I opt both D & B though I am not satisfied with the answer D. However, the key is “D.” I couldn’t understand why not B.Thanks in advance.[/FONT]

 

[emsr2d2]

[FONT=&quot]Hi, great people!
Could anyone help me with this question?
They couldn’t climb up the mountain because of the storm.
A. The storm made it not capable of climbing up the mountain.
B. Their climbing up the mountain was unable due to the storm.
C. The storm made them impossible to climb up the mountain.
D. The storm discouraged them from climbing up the mountain.

I opt both D & B though I am not satisfied with the answer D. However, the key is “D.” I couldn’t understand why not B.Thanks in advance.[/FONT]

B is not a correct sentence. It would have to read: "Their climbing up the mountain was impossible due to the storm".

"Climbing" cannot be "unable". Only a noun can be unable.

I am unable to speak Mandarin.
The table is unable to hold the weight of all the books.
My cat is unable to make a cup of coffee.

 

[fire fly]

Hi, emsr2d2!

Thanks for your prompt answer! I really appreciate it. However, I wonder if "Climbing" here is used as a gerund. Then, why isn't it considered is a noun here to be able to use with "unable"?

Many thanks!;-)