ありがとう Note the combination of "o" and "u", which is pronounced as a long "o". It's a result of to/と + u/う in this example. — Tae Kim's Japanese Grammar flashcard

こんにちは

Note that the Japanese "ha"-character (は) is pronounced "wa" in this case.

おはよう

The combination of "o" and "u" is usually pronounced as long "o". In Japanese, this can result from various character combinations (yo/よ + u/う in this example).

こんばんは

Again note that the Japanese "ha"-character (は) is pronounced "wa" in this case.

ありがとう ございます

おはよう ございます

すみません