Misc: what city was the site for the 1956 summer olympics?

Questions

The electric organs in an electric eel make up four-fifths of its ----------?

So that it can pull its lithe body into a tight, prickly little ball for defense, the hedgehog has a large muscle running along its ----------?

Some ----------?

There is a substantial wild population of golden hamsters living in Eastern Europe and the Middle East. Scientists speculate that all the domesticated golden hamsters in the world descended from a single female with twelve babies, which were dug from a burrow in Syria back in ----------?

There is approximately one ---------- for every human being in the world.?