"I agree with A c/d<1 - it can be 1 if c=d, if c/d =1 then 0 <= will fail, so II cannot be.
c^2 + d^2 > 1 is false, because
say c=.25 & d=0.5, c/d= .5 and is true for the inequality."
Read the statement carefully. I don't think that you can assume that C can equal D given the stated rule that 0<(1-c/d)<0. This implies that C must be another value besides D. In addition, c must also be < d. Also implicit in the statement given above, D is a positive number therefore C must be a positive number less than D - which makes c/d a fraction - a fraction is less than 1. Therefore, II must be true.
I don't think III MUST BE TRUE. C and D do not have to be integers - just greater than 0. If C = 1/3 and D= 1/2 then c/d = 2/3. And C^2 = 1/9 and D^2 = 1/4 combine the two fractions and of course the sum is less than 1.
read carefully. The stimulus states that 1 - c/d is greater then OR EQUAL to zero.
Former Senior Instructor, Manhattan GMAT and VeritasPrep
Vice President, Midtown NYC Investment Bank, Structured Finance IT
MFE, Haas School of Business, UC Berkeley, Class of 2005
MBA, Anderson School of Management, UCLA, Class of 1993