根据短文内容，判断下列句子的正误。你认为正确的句子请在题前括号内写“T”, 错误的写“F”。 When you go to the doctor's you may often have your eyesight checked. The doctor makes you read a chart with big and small 'E's'on it. Do you know where the chart came from? It's called the Snellen Chart. It was made by Herman Snellen, a Dutch doctor, in 1863. When reading the chart, you should stand five metres away from it. Your eyes should also be at the same height as the 10th line of letters. You should then read the letters from the top line to the bottom line. The letters get smaller as they get nearer the bottom. Doctors can find out if you are short-sighted, long-sighted, or if you have good eyesight, by the line which you can read. If your doctor thinks you need glasses, they'll tell you to go to hospital to get them . (     )1. The doctor often uses a Snellen chart to check your eyesight. (     )2. The Snellen Chart was invented by an American doctor. (     )3. When the doctor checks your eyesight, he will ask you to stand 5 metres away from the chart. (     )4. If you can only read a few big letters from the top, you probably are long-sighted. (     )5. The underlined word 'them'in the last line refer to (指) 'glasses'.