LOOKUP To Go From Numerics To Letters

I've used LOOKUP in the below and it works great.
LOOKUP(C8,{"A","A-","A+","B","B-","B+","C,","C-","C+","D"},{9,8,10,6,5,7,3,2,4,1})),)

But I've not been able to use that knowledge (or Excel help) to get the following to work.

LOOKUP(D108,{<1,>=1,<1.25,>=1.25,},{"D","C","C","")))...etc.
where D108 is in the range <1.0 to >2.0, and the letter grade must correspond to
D108 to Letter Grade
<1.0 D
1-1.25C
1.25-1.5B
1.5-1.75B+
1.75-2.0A
>2.0 A+