MONEYMAKING MACHINE: Google’s fourth-quarter earnings climbed 17 percent, even though a two-year slump in the Internet company’s average ad prices deepened and its Motorola Mobility smartphone operations suffered another big loss.

MOBILE CHALLENGE: Online ad rates have been falling because more people are clicking on smartphones and tablets. Marketers so far have been unwilling to pay as much for ads on mobile devices because they have smaller screens than personal computers.