U.S. stocks enjoyed a rally that pushed the S&P 500 back into positive territory for the year after Federal Reserve Chair Yellen stressed caution in raising interest rates. Yellen also said the fallout from market turmoil earlier this year on the economy looked to be minimal. Comcast's (CMCSA) - Get Report NBC has already sold $1 billion in national advertising for the upcoming summer Olympics. The Rio Olympics are one of the few when high-profile events such as track and field will be broadcast during North American prime time. LinkedIn (LNKD) moved cautiously higher despite Barclays downgrading the stock to EQUAL WEIGHT from OVERWEIGHT. Spices company McCormick (MKC) - Get Report climbed after raising its outlook following a better-than-expected first quarter.