YOU SAID:
I ate many cookies yestersay.
INTO JAPANESE
私は昨日クッキーをたくさん食べました。
BACK INTO ENGLISH
I ate a lot of cookies yesterday.
INTO JAPANESE
昨日はクッキーをたくさん食べました。
BACK INTO ENGLISH
I ate a lot of cookies yesterday.
You've done this before, haven't you.