doanbichngoc

“ 1. Three days aren't long enough for a good holiday
I can't find any mistake in this sentence.  aren't = isn't

2.The teacher ordered that the students stopped talking in class.
Is " stopped"? => had to stop.   stop  (bare infinitive)  actually, yours works too.

3. If you want to make your life worth living, make yourself useful for the country.
‘ For"=> To  correct

4.You should make your mother is happy for the rest of her life
" is"=> BE  Some would say "to be," but I think the correct answer would be to eliminate the "is" completely.  (is happy = happy)

5. I saw  the dog to run away.
To run=> run  correct

6. A wedding in Greek village is really worth to be seen
To be seen=> being seen  Yours is grammatically correct, but "seeing" would be more natural.

7.I sometimes wonder that my mother is really happy
That=> if  correct

8. In some countries it is usual for people have a siesta to talk.
Have=>to have  correct

9. Two- thirds of the money were spent on laboratory equipment.
Two-thirds-> two -third  were = was

10.Some of us are feeling that we are given too much homework.
Are feeling=>feel   correct    -    The sentence is also correct as is.

”

I don't think there's any good logical reason, but this is the way we deal with units idiomatically.  We look at this as an amount   -   a quantity.  "Amount" and "quantity" are singular.  "The quantity was insufficient."

Two hundred dollars isn't enough.

Do you think five gallons is enough gasolene to get us home?