[填空题]
Eclipses happen on Earth because of an amazing coincidenafvf5,i(( ucg ce. Calculate, a55 e6khrwa*lnbas15y)vk0q using the information inside the Front Cover, the angula5nseqky10a* )ra 5 wv6 lhb5kar diameters (in radians) of the Sun and the Moon, as seen on Earth. Sun = $rad$ Moon = $rad$