Breakdown of houmonbi wa getsuyou desu.
Questions & Answers about houmonbi wa getsuyou desu.
Because when は is used as the topic particle, it is pronounced wa.
So in this sentence:
- 訪問日 = topic
- は = topic marker, pronounced wa
- 月曜です = what is being said about the topic
This is one of the first big spelling-vs-pronunciation points in Japanese:
- は as a normal syllable = ha
- は as a particle = wa
