ご質問ありがとうございます。
① "I pretended as if nothing had happened."＝「何も起こらか無かったかのように振舞った。」
② "I acted as though nothing had happened yesterday."＝「昨日、何も起こらなかったかのように演技した。」
③ "I assumed an air of calm."＝「私は冷静を装った。」
ご参考までに。
I went about my business the next day as though nothing at all had happened.
I did my best to keep up appearances the next day.
この場合、次のような言い方ができます。
ーI went about my business the next day as though nothing at all had happened.
「何事もなかったかのように、次の日いつも通り過ごした」
to go about one's business「自分のすべきことをする」
as thought nothing at all had happened「何事もなかったかのように」
ーI did my best to keep up appearances the next day.
「次の日、なるべく平静を装うようにした」to keep up appearances「平静を装う」
ご参考まで！
I went about my business the next day as though nothing at all had happened.
I did my best to keep up appearances the next day.
この場合、次のような言い方ができます。
ーI went about my business the next day as though nothing at all had happened.
「何事もなかったかのように、次の日いつも通り過ごした」
to go about one's business「自分のすべきことをする」
as thought nothing at all had happened「何事もなかったかのように」
ーI did my best to keep up appearances the next day.
「次の日、なるべく平静を装うようにした」to keep up appearances「平静を装う」
ご参考まで！
アメリカ合衆国 
カナダ 
