The correct answer given is:
"Jet engine oil cooling through thermal exchange with
the fuel flowing from tanks."
This is badly worded, but as has been said previously we
can't change the question just because we don't like it.
The "oil cooling" is the only permanent result of the "oil to
fuel heat exchanger".
IF there is sufficient water present and IF the temperature is low enough it
will also prevent ice in the filter.
You seem to be coming to understand the frustrations we have in trying to teach
the syllabus to comply with the JAA system.