If \( y \) and \( x \) are reciprocals, then their product is equal to 1:
\[ y \cdot x = 1 \]
Given that \( y > 1 \), we can solve for \( x \):
\[ x = \frac{1}{y} \]
Since \( y \) is greater than 1, \( \frac{1}{y} \) will be less than 1. Therefore, \( x \) must be:
\[ x < 1 \]
Since reciprocals are positive when \( y > 1 \), \( x \) must also be positive, meaning \( x \) is between 0 and 1.
Thus, the correct answer is:
A. between 0 and 1.