Can we write SOQL query to fetch set the records which are in Trigger.New in before trigger?

what is reference variable in apex

trigger trigger_1 on Contact (before insert) {
List<Contact>contacts= trigger.new;
for(Contact c:contacts){
c.industry='naresh';
}
}

what is the mistake in this

what are the terms callin and callout in integration

what is the use of withsharing and withoutsharing and how can we implement them in user mode and system mode

Hello guys,

when we have to use system.runAs and runAs?