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