My dear and respected teachers,
1: "He has lots of female/females friends".?Should I use singular?
2: "May I ask the reason of not your visit". correct it please?
3: "I know that you can't speak English well but always try to make yourself understood". correct?
4: "I like scuba-diving". correct?
1. 'He has lots of girl friends' is more common. Instead of this, you may use 'female friends' - NOT 'females friends'. A compound noun's 'one word' becomes plural.
2. May I ask the reason for not visiting? OR
May I ask the reason why haven't you visited? OR
May I ask the reason why didn't you visit? - are used.
With 'reason' the correct preposition used is: 'for'
3. I know you can't speak English well but always try to understand - is correct.