• Complete sentence: Look at the weather report. It is going to rain cats and dogs.
- Bangla meaning: আবহাওয়ার রিপোর্টটা দেখো। মুষলধারে বৃষ্টি হতে যাচ্ছে।

• কোনো কিছু হতে যাচ্ছে, ঘটতে যাচ্ছে (Predictions) বোঝাতে be going to + verb এর base form ব্যবহৃত হয়।
- We use be going to to predict something that we think is certain to happen or which we have evidence for now.

- যেমন: Look at the weather report. It is going to rain cats and dogs. (The weather report provides clear evidence).
- এখানে 'is going to' ব্যবহৃত হবে, কারণ কোনো কিছু ঘটার ইঙ্গিত বা প্রমাণ আগে থেকেই আছে (যেমন: আবহাওয়ার রিপোর্ট)।

• অন্যদিকে,
ক) might have - refers to past possibility.
- যেমন: It might have rained yesterday.

খ) would - used for hypothetical situations or past habits.
- যেমন: It would rain every summer.

গ) Will
- "Will" is often used in a similar way to be going to.
- Will is used when we are talking about something with absolute certainty.
- অর্থাৎ, যখন সম্পূর্ণ নিশ্চয়তার সাথে কিছু সম্পর্কে বলা হয় তখন "Will" ব্যবহার করা হয়।
- যেমন: [An ‘A’ road is a main road. A ‘B’ road is a smaller road.]
- We are now very late, so we’re going to take the ‘B’ road. (The speaker refers to the present and emphasises the decision).
- I know the ‘B’ road will be quicker at this time of day. (The speaker states a fact- নিশ্চয়তা).

Source:
1. Oxford Dictionary.
2. Merriam-Webster Dictionary.