Solution:
Here, 'towards' means 'in favour of'. Hence it is the correct preposition to be used.

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Solution:
To walk down the street is to head towards a specific place. 'Run past' means 'to pass someone or something while running'. Hence option B makes the sentence meaningful.

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Solution:
The correct preposition to be used here is 'in'. In cases like this, 'America' is a place or location, so the preposition is 'in'.