Assuming this is 
A. When the value of b is less than 8, a is negative. 
b=7 a= 3.5 -4 = negative
b=7.9 a = #<4 - 4 = negative
b=0 a = 0-4 = negative
b=-1 a = -1/2 -4 negative - and note that as b becomes larger and larger negative a becomes larger and larger negative.
Statement A is true.
Check the others just to make certain.
B. When the value of b is greater than 8, a is negative. 
b=100, a=50-4 is positive.  NO!
C. When the value of b is less than 8, a is positive.   No - we saw that while evaluation A.  If b=0, a = 0-4 = negative.
D. When the value of b is greater than 4, a is positive.  No.  If b=5, a=2.5 - 4 = negative.
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