1. I / know / her / a long time
$\rightarrow$ I have known her for a long time.
2. They / buy / new house / April
$\rightarrow$ They have bought the new house in April.
3. My family / be / here / Christmas
$\rightarrow$ My family has been here since Christmas.
4. We / not see / each other / 10 years
$\rightarrow$ We haven't seen each other for 10 years.
5. How long / you ever / visit / Ha Long Bay ?
$\rightarrow$ How long have you ever visited in Ha Long Bay?
6. I / write / letter / 2 hours
$\rightarrow$ I have written a letter for 2 hours.