FIR filters, impulse responses and unit step function

[Jd303]

Hey everyone, the question I am faced with is this:

Which of the following expressions involving δ[n] is incorrect?
where "m" is a non zero integer and u[n] is the unit step function.

A. u[n-m] = δ[n] + u[n-m+1]

B. x[n]δ[n-m] = x[n-m]

C. δ[n] = u[n] - u[n-1]

D. δ[n]δ[n-m] = 0

I have been scratching my head for a while, but really not sure what to do. Any help as always would be greatly appreciated!

 

[rude man]

Hey Jd, take a shot at each of these, explain your rationale & then maybe we can be of help.