Select the word that best completes the sentences. Doctoral students who are preparing to take their qualifying examinations have been studying in the library night $—$the last three months.

Since এর ব্যবহার

নির্দিষ্ট সময়ের শুরু বোঝাতে ব্যবহার হয়
সাধারণত Present Perfect / Present Perfect Continuous tense-এ বসে

গঠন:
Since + point of time

উদাহরণ:

• I have lived here since 2015.
• She has been ill since Monday.
• It has been raining since morning.

For এর ব্যবহার

সময়ের পরিমাণ বা সময়কাল বোঝাতে ব্যবহার হয়
এটিও সাধারণত Present Perfect / Present Perfect Continuous tense-এ ব্যবহৃত

গঠন:
For + period of time

উদাহরণ:

• I have lived here for 10 years.
• He has been working for three hours.

• They have waited for a long time.

Since → কখন থেকে? (শুরুর সময়)

For → কতক্ষণ ধরে? (সময়কাল)