Plssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss Help!!!

What kind of shift is represented?
[tex]f(x)=2^{x-1}[/tex]
a.) vertical shift up 1 unit
b.) vertical shift down 1 unit
c.) horizontal shift left 1 unit
d.) horizontal shift right 1 unit
e.) no shift: vertical stretch by 3