Quickly catch up on the day's news

(CNN)Happy Pi Day! Here's what you might have missed on CNN today:

-- It's been one month since the Florida school massacre, and students across the country walked out of school to protest inaction over gun laws. Here's a recap of the walkouts, and here are some of the best photos from the day.
-- Attorney General Jeff Sessions is considering whether to fire former FBI Director Andrew McCabe, days before he is eligible to retire and collect a pension.
-- The Pennsylvania special election winner still has not been called, though Democrat Conor Lamb appears poised to claim victory.
    -- President Donald Trump will name a TV personality as the his new economic adviser.
    -- The UK will expel 23 Russian diplomats after concluding Russia is responsible for the attempted murder of a former spy.
    -- Stephen Hawking, considered by many to be the world's greatest scientist, died at 76. See his extraordinary life in pictures.
    -- Remember when HUD Secretary Ben Carson said he didn't select a $31,000 dining set for his office? Well, emails show the opposite to be true.
    -- United Airlines admitted the death of a dog that was asked to travel in an overhead bin was a "tragic accident."
    -- Angela Merkel has been sworn in as Germany's chancellor for a fourth term.
    -- The actress who played Queen Elizabeth in "The Crown" was paid less than her on-screen husband.
    -- Looking to make a big move? Here's the happiest country in the world.