Question

表示对于时 for与to的区别why are machines so important and necessary _

Answer 1

to and for us- this is just one example of a very tricky word..the truth is..both can be used in situation..but for this sentence...necessary for us is not commonly used in english conversation

for

is it useful for those students?correct

but

it was very useful to him- correct...

i can only say that to is better in this case..

both can be used..all make sense