Word formation
1. In ___ (desperate), some people decide to have an operation.
My answer is 'despair' but my teacher insists on 'desperation'.
2. They waste the ___ (value) time of doctors when really they are perfectly healthy.
My answer is 'invaluable' but my teacher insists on 'valuable' even though invaluable=valuable.
3. Of course it is ___ (advise) to use your common sense.
My answer is 'advised' but my teacher insists on 'advisable'.
4. You should be cautious when approached by strangers, and always keep in mind that violence is ___ (prevail) and that acting unafraid is the best protection against attack.
My answer is 'prevailing' but my teacher insists on 'prevalent'.

Am I wrong in all four places? Or perhaps both answers are possible?

ThanksEmotion: smile
Hi Rokas. have you tried looking up all these words in your dictionary, or in Webster?

I think you will find that your teacher is right in each case. Hope you didn't have a bet on it!
Hello, Rokas!

1. = "in desperation", or "when desperate": desperation is a noum, and only a noun can come after "in" (preposition) Emotion: sad
2. = "invaluable = so rare you can't give an exact value"; BUT the doctor's time value is evaluated (fees) so it's "the valuable time of doctors" Emotion: sad
3. "it is advised = people / we advise" / "advisable" is an adjective; I think both could work, but your teacher's choice is yet better
4. "violence is prevailing" here the verb "prevail" is conjugated in the progressive form; but "violence is prevalent" means that "violence is omnipresent", and I'm sorry to say it seems to be the better choice Emotion: sad

But I must say your suggestions were worth mentioning!
Teachers: We supply a list of EFL job vacancies

I tried the exercises without looking at your answers first.
In every case I instinctively chose the form your teacher chose.

Maybe all of us English teachers are wrong!

I would say that "in despair" was OK.

Nonetheless, the teacher has demonstrated the best answers, and in gapfills/multiple choices that is the important thing.
'Out of despair' might be more natural, if we wanted to use 'despair' in #1.

Students: Are you brave enough to let our tutors analyse your pronunciation?
'Invaluable' means 'unable to be valued', that is, so valuable that the doctor would not waste it on his patients, sick or healthy.

'Prevailing' means at the psychological instant of the discussion; 'prevalent' means generally, these days.

Thanks for the help. I was clever enough not to bet on these.Emotion: smile