RE:Homework They (Greece and China), and any other macro-forces, affect all stocks inasmuch as external valuations can affect overall PE ratios for all sectors.
https://en.wikipedia.org/wiki/Price%E2%80%93earnings_ratio#/media/File:S_and_P_500_pe_ratio_to_mid2012.png
If the market decides, for whatever reason, the PE average should be 75% of what it is today (they were roughly 40-45 in 2000), then you could enter a bear market even though earnings are steadily increasing. Those PE and sector multiples can be thought of a rollup of Greece, Ukraine, China, terrorists, drought, El Nina, ninjas, quantum foam fluctuations, and the Leafs winning the Stanley Cup. If PE ratios were locked at X for all sectors, then you wouldn't have to worry about Greece and China.