Convert the simple sentence into complex sentence by using adverb clause. I am thankful to you for helping my brother.
AI am thankful to you for helping.
BI am thankful to you because you helped my brother.
CI am too thankful to you.
DNone of these.
Complex sentence contains one main clause and one or more subordinate clause .
I am thankful to you - Main clause.
because you helped my brother- Subordinate clause.