Loss of words?
When we heard unexpected news, we were at a "loss for words". (there's NO "loss of words", I post the subject by accident)
A. couldn't speak for a while
B. didn't know what to say

Question

Loss of words?
When we heard unexpected news, we were at a "loss for words". (there's NO "loss of words", I post the subject by accident)
A. couldn't speak for a while 
B. didn't know what to say

Answer

I would say "at a loss FOR words" and it would mean B - you COULD speak, but didn't know what to say.

Answer

This is a terrible exercise!

1. The English is wrong. The correct expression is 'at a loss for words.'
2. Both answers are possible - you were shocked, so you couldn't speak because you didn't know what to say at that moment.

Answer

Great !
at a loss for words 
It means impotent to think of something to say
If I was alone with you, I'd feel at a loss for words.