Укажите пары значений \(\displaystyle z\) и \(\displaystyle t{\small,}\) при которых выражение \(\displaystyle \frac{z+t}{zt}\) не имеет смысла.

• \(\displaystyle z=0{\small;} \) \(\displaystyle t=5\)
• \(\displaystyle z=20{\small;} \) \(\displaystyle t=0\)
• \(\displaystyle z=-2{\small;} \) \(\displaystyle t=2\)
• \(\displaystyle z=0{\small;} \) \(\displaystyle t=0\)