Answer:
If you look at the coordinates of Iceland, they are 64.9631° N, 19.0208° W. This is quite a far distance from the equator, meaning that it does not receive as much sunlight as other location on earth that are closer to the equator. The reduced sunlight of the country means that it will be much cooler than other countries that are closer, as seen from the daily temperature, maxing out at just above 10 degrees Celcius. Iceland is also a country that has a high elevation, and from what we know about geography, the higher in altitude you go, the thinner the air and the cooler it is.
In Greece, it is much closer to the equator than Iceland is, meaning that it receives more sunlight. This shows why its average temperature in summer peaks at above 30 degrees Celcius instead of the 10 in Iceland. Greece also has a widly varying altitude across the country, so some places are closer to sea level, meaning that the air is thicker, so it would absorb more heat resulting in its higher temperatures.
For the rainfall parts, I'm sure you can work why it is like that from the information above.
