By reading regularly, you can improve your vocabulary. (Make it complex)

• Correct Answer: ক) If you read regularly, you can improve your vocabulary.

• By / In case of / In the event of + gerund যুক্ত Simple Sentence কে Complex Sentence করার নিয়ম:
- By / In case of / In the event of এর পরবর্তী gerund (যেমন: studying, reading, working, etc.) বাদ যাবে এবং If দিয়ে Complex Sentence এর শুরু করতে হবে।
- ২য় clause এর Subject বসবে।
- Verb + ১ম Clause এর বাকী অংশ বসে।
- ২য় Clause- টি অপরিবর্তিত থাকবে।

Simple Sentence: By reading regularly, you can improve your vocabulary.
Complex Sentence: If you read regularly, you can improve your vocabulary.

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