Im having trouble with my homework so here is the question; which of the following is the graph of an arithmetic sequence whose first term is 1 and whose common term is 0.5

Well, first of all, here's a tip on how to read problems:
Whenever the question says "Which of the following ...",  that always means
"Here are some choices.  Now YOU choose the correct one."
It should be pretty obvious that when you ask someone to help you
answer the question, you should also show him the choices.

On the graph, the x-axis is marked 1, 2, 3, ... up to at least 15,
representing the terms.

The y-axis is numbered to represent the values of the terms.

The graph of the arithmetic sequence you described starts at the
point (1, 1).  From there, it's a line that rises with slope = (0.5 per term).

Since it's an arithmetic sequence, it's not actually the whole line, because
the sequence only exists at whole-number terms.  I mean, there's no such
thing as the value of  "term number 2.6"  or "term number 4.013". 

So the graph of the sequence is actually all the dots at the points over
the whole-numbers on the x-axis. 

(But it's OK if the graph shows the solid line, because if you think about
it, nobody is going to be using the graph to look for the value of term
number 7.51 !)

Iknow one of the answers is a and maybe b but not 100% sure about b

I’m not sure what it is i sorry : ((