3.　 potatoes

2.　 zoos

1.　 factories

20.　　 Do scientists always count __________ their fingers.

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19.　　 Go __________ the stationers and get some stationery.

18.　　 These cakes taste __________ cement.

17.　　 It's nice __________ you to take him __________ hospital.

16.　　 It's difficult __________ them to study English because they aren't interested __________ it.

15.　　 What do you mean __________ the word "stupid"? It's another way __________ saying "foolish".

14.　　 How did you travel? We travelled __________ air.