Most of those questioned refused to answer

[nelson13]

In English, we can say

Most of those questioned refused to answer.
(=Most of those who were questioned refused to answer.)

and

Those present were in favour of change.
(=Those who were present were in favour of change.)

but for

1.Opportunities are for those who are well prepared.
2.Those who are rich can do many things.
3.He only helped those who were aged.

you cannot leave out the red words;but for

He only helped those who were aged between 70 and 90

you can omit the red words.

Also, for

We should help thosewho are in need

you can ellipt the red words.

I can't think of a general rule why and when these red words can be omitted.

Could anyone help me?

[philo2009]

In English, we can say

Most of those questioned refused to answer.
(=Most of those who were questioned refused to answer.)

and

Those present were in favour of change.
(=Those who were present were in favour of change.)

but for

1.Opportunities are for those who are well prepared.
2.Those who are rich can do many things.
3.He only helped those who were aged.

you cannot leave out the red words;but for

He only helped those who were aged between 70 and 90

you can omit the red words.

Also, for

We should help thosewho are in need

you can ellipt the red words.

I can't think of a general rule why and when these red words can be omitted.

Could anyone help me?

The general rule is that is is normally possible where the form after 'those' is a participle, and normally not so where it is an uncomplemented adjective.

Complemented adjectives, however, are normally allowable, hence

Those happy with the proposed pay hike were among the first to turn up.

(where 'happy' is complemented by 'with...hike')

or

Those rich in spirit are superior to those rich merely in terms of money.

while we may not have simply

*Those happy were...

or

*Those rich are...

'Present' and 'absent' are among a small number of apparent exceptions, although we may rationalize this on the basis that a complement is always implicit (present at the meeting, absent from the meeting, etc.)