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This is case of simple present tense

When we talk about two past events simultaneoulsy , the event happend first takes past perfect tense

Since we are talking about future "by next january" hence, we will use future perfect continous tense.

The phrase 'In my youth' refers to a completed period in the past. Therefore, the simple past tense 'took' is the most appropriate choice to describe a habitual action in the past.

The past perfect tense 'had sold' is used to describe an action that was completed before another action in the past (becoming a famous inventor).

When there are two events occured in past , the event which occured first takes past perfect tense.

In questions using the auxiliary verb 'did', the main verb must be in its base form. Thus, 'see' is the correct choice.

Case of simple present tense

The present continuous tense is often used to describe a planned future arrangement. 'Is leaving' correctly indicates a scheduled departure for this evening.

Case of past perfect continous tense

The phrase 'for ten years now' indicates an action that started in the past and continues to the present, requiring the present perfect tense.

In questions starting with 'Does', the main verb must be in the base form. Therefore, 'know' is the correct choice.

The construction 'could have' followed by a past participle is used to express a possibility in the past that did not happen. 'Have married' fits this structure.

After the modal verb 'will', the base form of the verb is required. 'Know' is the correct base form.

 Distinction means 'difference'.