Find out whether there is any grammatical error in below sentence.
Having received your letter / this morning, we are writing / to thank you for the same.
A. Having received your letter
B. this morning, we are writing
C. to thank you for the same
D. No error
Answer: Option D

how on the second part of sentence is correct
Remove to....thank you for the same
Instead of using 'we are waiting' ,using 'we have been waiting'is more appropriate.