Bonjour,

a) How much did you pay for that guitar ?

L'auxiliaire est déjà au prétérit.

b) Were you playing tennis when it started raining ?

Concordance des temps

c) Who did you phone at 10 o'clock this morning ?

Auxiliaire puis sujet puis verbe

d) Did John pass his exam ?

L'auxiliaire est déjà au prétérit.

e) What were you doing when the lights went out ?

You : were, pas was

Bonjour,

Réponse :

a) How much did you payed for that guitar?

  How much did you pay for the guitar?

( Question au prétérit, la marque du prétérit est dans l'auxiliaire "did" , le verbe doit être non conjugué )

b) Were you playing tennis when it starts raining?

  Were you playing tennis when it started raining?

( conncordance des temps prétérit Be + V-ing   et prétérit simple - action courte )

c) Who did phone you at 10 o'clock this morning?

  Who phoned you at 10 o'clock this morning?

( Ici pas d'auxiliaire car "who" est sujet. Lorsqu'une phrase commence par un mott  interrogatif servant de sujet au verbe, celui-ci se met à la forme affirmative, sans auxiliaire . Ici au pétérit )

d) Did John passed his exam?

   Did John pass his exam?

( Question au prétérit, la marque du prétérit est dans l'auxiliaire "did" , le verbe doit être non conjugué )

e) What was you doing when the lights went out?

  What were you doing when the lightts went out?

( Le sujet est "you" donc le verbe "be" : were )