1. Helen .. (mop) the floor at the moment. 2. (dust) the furniture every week. 3. You shouldn't (eat) so many sweets. 4. The police (catch) the burglar yesterday. 5. They (study) at two o'clock yesterday. 6. I think you (have) a great time in Mexico next month. 7. If we (not hurry), we will miss the bus. 8. If I won a lot of money, I (travel) around the world. 9. Mary ... (live) in this neighbourhood since she was a child. 10. The phone rang while I (have) dinner.

1. Helen is mopping the floor at the moment.
To form a sentence in the present continuous tense, we use the verb "to be" in the present tense (is, am, are) followed by the present participle (base verb + -ing). In this case, the base verb is "mop," so we add -ing to make it "mopping."

2. We dust the furniture every week.
In this sentence, the subject pronoun "we" is used. When talking about a habitual action, we use the base form of the verb "dust" without any additional endings.

3. You shouldn't eat so many sweets.
In this sentence, we are giving advice using the modal verb "should" and the base form of the verb "eat."

4. The police caught the burglar yesterday.
Here, we are talking about an action that happened in the past, so we use the simple past tense. The base form of the verb "catch" is used, and we add -ed to form the past tense.

5. They studied at two o'clock yesterday.
Similar to the previous sentence, we are talking about an action that happened in the past, so we use the simple past tense. The base form of the verb "study" is used, and we add -ed to form the past tense.

6. I think you will have a great time in Mexico next month.
In this sentence, we are using the future tense to talk about a future event. The base form of the verb "have" is used, and we add the modal verb "will" before it.

7. If we do not hurry, we will miss the bus.
Here, we are using a conditional sentence to express a hypothetical situation. The verb "hurry" remains in the base form, and we use the future tense with the modal verb "will" to indicate a possible outcome.

8. If I won a lot of money, I would travel around the world.
This is another conditional sentence expressing an unreal or hypothetical situation. The verb "win" is in the past tense, and we use the past tense with the modal verb "would" to indicate the unreal outcome.

9. Mary has lived in this neighborhood since she was a child.
In this sentence, we are using the present perfect tense to talk about an action that started in the past and continues in the present. The base form of the verb "live" is used, and we add the auxiliary verb "has" before it.

10. The phone rang while I was having dinner.
Here, we are using the past continuous tense to talk about an ongoing action in the past that was interrupted by another action. The verb "have" is in the past continuous form, with the verb "be" in the past tense (was/were) followed by the present participle (eating).