Text: While some gold medals are solid gold, others are gold-plated or silver-gilt, like those of the Olympic Games, the Lorentz Medal, the United States Congressional Gold Medal and the Nobel Prize medal. Nobel Prize medals consist of 18 karat green gold plated with 24 karat gold. Before 1980 they were struck in 23 karat gold.

Question: are the olympic gold medals made of real gold?

Options:
(a). no
(b). yes
(b).