Help..confused about names in air ticket booking online

[clicknick]

Hi,
My name is typical chinese, eg: TAN AH KOW

When I purchase tickets from airlines online, I am asked to fill in exactly as per passport (and cannot have space like AH KOW), and different airlines have different options:

1)
FIRST NAME: LAST NAME:
2)
FIRST NAME: LAST NAME (SURNAME):
3)
FIRST NAME: LASTNAME (FAMILY NAME):

So my question is, do I fill in
VARIANT 1
1)
FIRST NAME:TAN LAST NAME: AHKOW
2)
FIRST NAME:TAN LAST NAME (SURNAME):AHKOW
3)
FIRST NAME:TAN LASTNAME (FAMILY NAME):AHKOW

OR
VARIANT 2
1)
FIRST NAME:AHKOW LAST NAME: TAN
2)
FIRST NAME:AHKOW LAST NAME (SURNAME):TAN
3)
FIRST NAME:AHKOW LASTNAME (FAMILY NAME):TAN

OR
VARIANT 3
1)
FIRST NAME:TAN LAST NAME: KOW
2)
FIRST NAME:TAN LAST NAME (SURNAME):KOW
3)
FIRST NAME:TAN LASTNAME (FAMILY NAME):KOW

OR
VARIANT 4
1)
FIRST NAME:KOW LAST NAME: TAN
2)
FIRST NAME:KOW LAST NAME (SURNAME):TAN
3)
FIRST NAME:KOW LASTNAME (FAMILY NAME):TAN

 

[TMC]

Just remember last name/family name means surname, that one would be Tan in your example. you can fill in as Ah Kow or Ahkow, they normally dont really bother.