<Tr> <Td> 1988 </Td> <Td> USA </Td> <Td> Martina Navratilova </Td> <Td> Martina Navratilova / Pam Shriver </Td> </Tr> <Tr> <Td> 1989 </Td> <Td> USA </Td> <Td> Martina Navratilova </Td> <Td> Helena Suková / Jana Novotná </Td> </Tr> <Tr> <Td> 1990 </Td> <Td> TCH </Td> <Td> Helena Suková (3) </Td> <Td> Helena Suková / Jana Novotná </Td> </Tr> <Tr> <Td> 1991 </Td> <Td> TCH </Td> <Td> Jana Novotná (4) </Td> <Td> Gigi Fernández / Jana Novotná </Td> </Tr>

Who's ranked number one in women's tennis