Is it ok to answer only the day of the month to the question "今天几号?"?
First dialog:
-- 今天几号?
-- 今天是八月二十号. (it is OK, common phrase)
Second dialog:
-- 今天几号?
-- 今天是二十号. (is it Ok? Why not?)
If the second dialog is not grammaticaly correct, how can I ask for a day of the month?
UPDATE:
It is ok to use month when asking 你的生日是几月几号? But the date (month + day) is asked without month (from book 汉语会话301句) just 今天几号?
If I was asked 今天几号? , most likely I will just answer 20号 or 今天20号. I would assume someone is expecting a brief answer since he'd asked briefly. You can also answer 今天是八月二十号, just like your first dialogue.
If they are also unsure about the month, they might come back with something like, 这是几月了？ or 这个月是几月？. I might just answer: 8月 or 这个月是8月.
If they want to ask the exact month and date of today, they might put "今天是几月几号？". The answer would be "今天是8月20号？" or just "8月20号？".
Yes, it totally makes sense to answer only the day since the question is asking for the day only instead of month and day.
If one is asking for month it would be something like: 今天是几月几号？
Responding only the day is based on you both are very clear about the current month. Even in English we can here something like: "How is Danny?" "Fine." Based on we all know who we are talking about. But if you drive a time machine to a new world and has no idea what the month is, you can then ask "Sorry, what month are we talking?"
