By putting suitable signs + , − , × , ÷ , ( , ) in-between the digits 8 8 8 8 one can generate many numbers. For example, 8 × (8 + 8) + 8 = 136. Which of the following numbers cannot be generated this way?
a.  9

b.  7

c.  4

d.  5

e.  8

f.  6

g.  10