help need with tense please!!

[Clara]

hello!

i have problems understanding the sentence here. my teacher gave me this sentence and for next lesson i must prepare something to say about it : ( i confused because i dont know what is the object or subject. this is passive yes? what is the subject is it "them"?

the problems many of them face are more difficult than has been appreciated until now.

gracias!!

[Alan]

Yes, this is a structurally "tricky" sentence!

In the subordinate clause, a subject 'it' - essentially referring back to the whole of the main clause - is implied but obligatorily omitted.

Thus the overall meaning is that the degree of difficulty of these problems was not fully appreciated (i.e. understood) by people until recently.