The box was too heavy to lift. (Complex)

- Simple: The box was too heavy to lift.
- Complex: The box was so heavy that I could not lift it.

• Too + --- + to যুক্ত Simple sentence- কে Complex sentence এ পরিবর্তনের নিয়ম:
- Subject + verb এরপরে প্রথম too এর জায়গায় so বসে।
- Too + --- + to এর মাঝের Adjective word টি বসে।
- that বসে।
- প্রথম subject টি বসে।
- tense অনুযায়ী can not/ could not বসে।
- to উঠে যায় ।
- বাকী অংশ বসে।

• More example:
- Simple: Akash is too sick to go outside.
- Complex: Akash is so sick that he can not go outside.

Source: Advanced Learner's Communicative English Grammar & Composition By Chowdhury & Hossain.