[填空题]
Estimate the number of (a)f 5h,1n ;f/0zqcpolwj 7:i0xr .iwy qxmoles, $ \times10^{22 }$ moles and (b) molecules of water in all the Earth’s oceans. Assume water covers 75% of the Earth to an average depth of 3 km. $\approx$ $ \times10^{46 }$ molecules