Vocabulary, word
      Vocabulary means "a set of words." Therefore, we should say Peter has a large vocabulary or Peter knows many words, and NOT Peter has many vocabularies.
      Alphabet, letter
      An alphabet is a set of letters. In the English alphabet, there are 26 letters (NOT alphabets).
      Altogether, all together
      Altogether = totally 例句：There are altogether 15 students in our class.
      All together = in a group 例句：They are all together in the sitting room.
      Arrive, reach
      Arrive 例句：He arrived in Vancouver after a 12-hour flight. He arrived at the airport two hours earlier.
      Reach 例句：He reached Vancouver after a 12-hour flight.
      Lie, lay
      Lie/lying/lay/lain （躺下；橫放）
      例句：You look tired. Lie down and rest.
      例句：The old painting has been lying there for years.
      Lie/lying/lied/lied = not tell the truth
      例句：He lied to his parents.
      Lay/laying/laid/laid（放置；生蛋）
      例句：Lay ( = put down) the book on the table.
      例句：Hens lay eggs. Our hen laid a big egg yesterday.

      Exercise
      Fill in the spaces with suitable words. In some items, you may have to change the words into the correct form or tense. （在空位內填上適當的字，有些地方可能要用上正確的格式或時式）
      1. altogether/all together
      (a) Pile up the books and then tie them ____________.
      (b) How many books are there ____________.
      2. lay/lie
      (a) I ________ the book on the table. Now it is ________ on the table.
      (b) The hen has ________ an egg. 
      (c) Yesterday he ________in bed until eleven o'clock in the morning.
      (d) __________ down and rest.
      (e) He has _________ to you.

      Answers:
      1. (a) all together    (b) altogether
      2. (a) lay, lying     (b) laid    (c) lay    (d) Lie    (e) lied