Question

Put the verbs in the right verb-form 1. Nobody (can) explain why David (to fly) to Paris without hiswife.2. He told us that he (to invite) Mary to our party if he (to see)her.3. It (to rain) since I (to get up) in the morning.4. When we (to enter) the room he (to read) a letter.5. There (to be) no doubt that he (to know) the truth.6. Marry (to arrive) from Rome three days ago, and (to leave)for Paris it once.7.1 (to see the signal, so I (to stop).8. We (to go) to the country as soon as it (to stop) snowing.9. We (to find out) that somebody (to break into) our house.10. What he (to do) when you (to call on) him.​

Answer 1

1 could, had flown // can, has flown

2 would invite, saw

3 has been raining, got up

4 entered, was reading

5 is, knows // was, knew

6 arrived, left

7 saw, stopped

8 will go, stops

9 found out, had broken into

10 was he doing, called on

Answer 2

The sentences you provided are examples of conditional sentences in English. They express different hypothetical situations, and the verbs in them should be in the base form. Here is the correct form of the sentences:

1. Nobody can explain why David can fly to Paris without his wife. 2. He told us that he would invite Mary to our party if he saw her. 3. It has been raining since I got up in the morning. 4. When we entered the room, he was reading a letter. 5. There is no doubt that he knows the truth. 6. Mary arrived from Rome three days ago, and she left for Paris once. 7.1 (To see the signal, so I stopped.) 8. We want to go to the country as soon as it stops snowing. 9. We found out that somebody broke into our house. 10. What he would do when you called on him.

Please note that in English, the present perfect tense is often used to talk about actions that happened at an unspecified time before now. In the sentence "It has been raining since I got up in the morning", "has been raining" is the present perfect tense.

In the sentence "There is no doubt that he knows the truth", "is no doubt" is a phrase that expresses certainty about something, and "knows the truth" is in the base form because it is not part of a conditional sentence.

In the sentence "Mary arrived from Rome three days ago, and she left for Paris once", "arrived" and "left" are in the past simple tense because they refer to specific times in the past.

In the sentence "We want to go to the country as soon as it stops snowing", "want to go" and "stops snowing" are in the base form because they are part of a conditional sentence.

In the sentence "We found out that somebody broke into our house", "found out" is in the past simple tense because it refers to a specific time in the past, and "broke into" is in the past participle form because it is part of a passive voice sentence.

In the sentence "What he would do when you called on him", "would do" is in the conditional perfect tense because it expresses a hypothetical situation in the past.