STOCKS SINK: Here's what you need to know

Stocks extended their losses from late last week when Britain's unexpected vote to leave the European Union cratered global markets.
The pound also fell further against the dollar.
First, the scoreboard:
Dow: 17,140.24, -260.51, (-1.50%)
S&P 500: 2,000.54, -36.87, (-1.81%)
Nasdaq: 4,594.44, -113.54, (-2.41%)
WTI crude oil: $46.33, -$1.31 (-2.75%)
US 10-year yield: 1.461% (-0.118)
S&P downgraded the UK's credit rating from "AAA" to "AA": Because of Brexit, th