Explanations

  1. The tourist is the receiver of the action, as the funnel web spider did the biting. Therefore this sentence is in the passive.
  2. Although there is no mention of who did the observing, the schoolchildren are the receivers of the observing and therefore this sentence is also in the passive. Explicit mention of the 'doer' of an action in a passive sentence is optional in English.
  3. This sentence is in the active voice. The astronomers (the subject) are the ones carrying out the action of monitoring.
  4. "You" are the receiver of the action of being served, so the sentence is in the passive. Once again there is no mention of the person 'doer' of the action of serving.
  5. The subject of the sentence (the dingo) is the one carrying out the action, and therefore the sentence is in the passive.
  6. "I" am offering to help, so this sentence is also in the active voice.
  7. The housebound are the receivers of the action and therefore the sentence is in the passive voice.
  8. "You" are one ones not working hard enough, making this sentence an active one.
  9. "We" are the receivers of the action (the heat prevented us), so this is a passive sentence.
  10. "They" are the 'doers' of the action of talking, and therefore this sentence is in the active voice.
  11. This sentence can be turned around to say: They threw a party for me. Party is the direct object (what did they throw?), and therefore "me: is the indirect object.
  12. The question "What did he read?" can be asked about the book, so it is the direct object in this sentence.
  13. The teacher gave (what?) a lecture to the student. The student is the indirect object in this sentence.
  14. The question "What did the parents buy?" can be asked, so car is the direct object.
  15. The question "What did you show to me?" can be asked, so this is the direct object.
  16. This sentence can be re-written as "That taught (what?) a lesson to you. Therefore "you" is the indirect object in this sentence.
  17. The preposition "to" before "me" helps to make it clear that "me" is the indirect object in this sentence.
  18. The bank did not lend (what?) any money... Therefore, any money is the direct object of this sentence.
  19. This sentence can be re-written as I give (what?) my word to you. Therefore, my word is the direct object.
  20. This sentence can be re-written as: "We'll send a postcard to you." Thus, "you" is the indirect object.