The answer is “おはよう(Ohayoo)”.
The polite form of “おはよう(Ohayoo)” is “おはようございます(Ohayoo-gozaimasu)”
while “こんにちは(Konnichiwa)” and “こんばんは(Konbanwa)” work both as casual form and as polite one.
We can use “おはよう(Ohayoo)” to our friends and our family,
but we should use “おはようございます(Ohayoo-gozaimasu)” to the elder people or in the business situation.
See you tomorrow!