阅读下面材料，在空白处填入适当的内容（1个单词）或括号内单词的正确形式。
Imagine life as a game in which you are playing some five balls in the air. You name (1) (they) — work, family, health, friends and spirit, and you’re keeping all these balls in the air.
You understand that work is a rubber ball. If you drop it, it will bounce (弹) back. (2) the other four balls are made of glass. If you drop one of them, it will be damaged or even broken to (3) (piece). They will never be the same. You must understand the balance in your life. How?
Don’t compare yourself with others. It is because we are different and each of us is special. Don’t set your goals by what other people consider important. Only you know (4) is best for you. Don’t give (5) when you still have something to give. Nothing is really over until the moment you stop trying. Knowledge is (6) weightless treasure you can always carry (7) (easy). Don’t run through life so fast that you forget not only where you’ve been, where you are, but also where you will go.
Life is not a race, but a journey to be enjoyed slowly each step of the way. Yesterday is history, tomorrow is a mystery, and today is a gift. That’s (8) we call it the present.
(9). As Polly observed the passengers on the train, she had a feeling that she ________ (watch) by a tall man in a dark overcoat.
(10). Don’t be frightened by sharks as you are 30 times more likely________ (hit)by lightning than be attacked by a shark.
(11) It was in war________they found pigeons’ greatest use.
(12)However, the Norman Conquest did not affect English as much as the Angles and the Saxons’ victory about 600 years earlier, which led to Old English ________ (replace) Celtic.
(13) Both the English language and the English people are named ________ the Angels.
(14)Keep your parents ________ (inform) how you are getting along with your studies, or they’ll be worried about you.
(15)However, by the latter half of the 14th century, English________(come) into widespread use among all classes in England.