A box contains only green and yellow balls. You pull out one ball without looking.
What color must it be?
Which spacecraft was the first to successfully land humans on the Moon?
Who wrote To Kill a Mockingbird?
Which organ is responsible for pumping blood throughout the body?
Which number is both even and prime?
What is the value of 12 × 8 − 15?
Which process gradually wears away rocks and soil?
Which habit is most effective in reducing the spread of many infectious diseases?