Possibility and permission

Possibility:
It could arrive soon Po ygo prom
It could be rain Po ran
It could be Po so
Capacity:
I am not able to N po
I don't know how to make it N sao fao
To ask:
Can I come today? Po do oy?
Can you return tomorrow? Po bolbo mn?
To give and to refuse permission:
Here you can Kui T po
Here one cannot smoke Kui n po
To use the verb po:
I can help you Po sok T
I cannot help you N po sok aT
To use the verb sao:
She doesn't know to read La n sao ldo
To use the verb so + povi:
Is it possible to speak with you?   So povi dso c ut?
I am sorry, it is not possible Y trusi, n so povi
Is it possible to buy tickets? So povi kafo tras?
Of course that it is possible Xs so povi