When I was preparing for my FCE exam I came across a task which I cannot really fully understand. The task was the word transformation. I got it all right, except only one. The sentence was:
Then again, celebrities often do seem to lead such interesting lives that it is perhaps ____(understand) that we want to find out more about them
So I put 'understood' here, but it turned out that 'understandable' was a correct answer. I cannot understand why. For example it's correct to say:
It was understood that taxes would increase dramatically
Here we have a passive form of the verb understand, but probably this sentence is correct due to the past simple?
Well, we can say:
It is done
Here we have the passive form of the present, but this sentence is still correct. In my opinion, we have to use 'able' adjective instead of the passive form, when we can substitute the verb with an adjective. Is it so? Am I missing something?