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Solution:
We use 'at' for a precise time, 'in' for months, years, centuries and long periods and 'on' for days and dates.

Solution:
'Indulge in' means 'to become involved in (something, especially something that is considered wrong or improper)'. Hence it makes the sentence meaningful.

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Solution:
'Towards' means 'in the direction of'. Hence it makes the sentence meaningful.

Solution:
Here 'with' means 'be with somebody (on something)'. Hence it makes the sentence meaningful.