TITLE: Why is the sample correlation coefficient not $1?$
QUESTION [0 upvotes]: A reasonable value for the sample correlation coeffcient
  $\rho$
  between daily maximum tem-
  peratures and daily ice cream sales would be
$A) 0$
$B) 1$
$C) 0.7$
$D) -0.7$

I am taking intro stats for the first time and this was a question that confounded me. 
I know the answer is neither $A$ nor $D$. So stuck between $B$ and $C$, I chose $B$. The correct answer was $C$ - indicating the correlation isn't that strong.
I am assuming the higher the temperature, the higher the sales? Indicating some sort of straight linear trend - strong correlation
?

REPLY [2 votes]: If the correlation was $0.7$, then the correlation is fairly strong. It wouldn't be $1$, because that would mean there would be a direct/"perfect" relation between the two.
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