Many years have passed since ____________.

• "Many years have passed since we graduated from college."
--------------------

• Since এর প্রথম অংশ Present Indefinite/ Present Perfect Tense হলে পরের অংশ Past Indefinite Tense হয়। 
- যেমন:
1. Many years have passed since his father died. 
2. It is many years since I went there.

• প্রশ্নে উল্লিখিত বাক্যটিতে since এর পূর্বের অংশ Present Perfect Tense (Many years have passed) এ আছে বিধায় পরের অংশ Past indefinite tense ( we graduated from college.) হয়েছে।
=================== 
• আবার Since এর প্রথম অংশ Past Indefinite Tense হলে পরের অংশ Past Perfect Tense হয়। 
যেমন: 
- It was many years since they had first met.