Can a CA doing tax audits conduct internal audits?

HELLO FRIENDS!!! I WOULD LIKE TO KNOW SOMETHING INTERESTING

RECENTLY I WAS SURFING WEB AND I CAME ACCROSS THIS NAME -

"THE INSTITUTE OF CERTIFIED INTERNAL AUDITORS!"

HEY EXPERTS OUT THERE - PLEASE SHARE YOUR KNOWLEDGE AND TELL ME...

1) WHO IS A CIA?

2) IS A CHARTERED ACCOUNTANT, A CIA BY DEFAULT? IF NO CAN HE GIVE THIS CERTIFICATION EXAM?

3) IF ANS TO ABOVE IS NO, THEN PLS TELL ME - ARE THE BIG FOUR FIRMS ONLY INTERNAL AUDITORS OR THEY ALSO CONDUCT EXTERNAL AUDITS?

4) DO THE BIG 4 FIRMS CONDUCT TAX AUDITS AND STATUTORY AUDITS? IF NO WHAT IS THE REASON PLS TELL ME????

THANKING YOU AND REGARDS IN ADVANCE... PLS PLS PLS HELP ME TO LEARN ABOUT THESE AND SHARE YOUR KNOWLEDGE... IT WILL BE HIGHLY APPRECIATED...