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はもちろんのこと

not to mention

→ は
phrase Rare #38,370
not to mention Used to say that the first item is obvious or expected, and to emphasize that the following item also applies. Often appears in the pattern 「Aはもちろんのこと、Bも」, meaning “not only A, but also B.”
JA: 彼は日本語はもちろんのこと、中国語も話せます。
EN: He speaks not only Japanese, but also Chinese.

彼は英語はもちろんのこと、スペイン語も話せる。

He can speak Spanish as well as English.

彼が承諾するのはもちろんのことだと思った。

I thought it was a given that he would agree.

彼は英語はもちろんのことドイツ語も話す。

He speaks German, not to mention English.

彼女はピアノはもちろんのこと、バイオリンも弾ける。

She can play the violin, not to mention the piano.