Answer:
I believe it is A) Telegraph
Step-by-step explanation:
The key point to look out for is the decade they are asking which in this case is 1840s!
Looking at the telephone, that was not invented until the 1870s so B cant be the answer.
Choice C has nothing to do with communications so that definitely can't be it either.
Television is more for entertainment rather than communication.
Thus, through the process of elimination, the answer is A!
I hope this helps :)