<span>a. DA
Given the question and available options, this looks like a question about Ethernet frames. So let's look at the options and see what makes sense.
a. DA
* DA - Destination address. And the question pretty much defines what it is. So this is the correct choice.
b. SA
* SA - Source address. This is the physical address that the frame was sent from. And since the question is mentioned who the frame is intended for, this is obviously the wrong choice.
c. SFD
* SFD - Start Frame Delimiter. This is a special CONSTANT sequence of bits that terminates the preamble. It's purpose is to indicate the start of the frame payload. Since it's a constant value, it does not indicate in any way where the frame is intended to go. So this is a bad choice.
d. Preamble
* Preamble - is a pattern of alternating 0 and 1 bits intended to synchronize receivers so that the rest of the frame is interpreted correctly. This too is a constant value and as such can't indicate the destination of the frame, so it's a bad choice.</span>
