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Hello.
I'd like to know what is the function of the prepositions in these sentences. Why do you need it? How can they be rephrased for a better understanding?
I use this knife to slice vegetables with.
Are you being attended to?
The bank was robbed and the safes were broken into.

They don't seem to be part of the pattern of a relative clause like this:
He is the man she works with. > He is the man with whom she works.
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LatinHello.
I'd like to know what is the function of the prepositions in these sentences. Why do you need it? How can they be rephrased for a better understanding?
I use this knife to slice vegetables with.No preposition needed.
Are you being attended to?See below
The bank was robbed and the safes were broken into.See below

They don't seem to be part of the pattern of a relative clause like this:
He is the man she works with. > He is the man with whom she works.

I work on the premise that "break" and "break into" are two separate verbs, the latter being a two-word verb, rather than a verb with a preposition. The same with "attend" vs. "attend to". "Turn on the radio", for example, is clearly a separate entity, not really related to the verb "turn". I think this makes the whole question much easier to deal with [with which to deal, if you insist].
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American English has many phrasal verbs or verbs with preposition. Therefore, we have slice with, attend to, and break into.

Slice with is not a true phrasal verb since “with” is an optional preposition.

We use the knife to slice the bread => We use the knife to slice the bread with => is rather redundant.

However, “with what do you slice the bread?” or “what do you slice the bread with?”

On the other hand, “attend” and “attend to” have different meanings

I attend school during the day, and attend to my sick brother in the evenings.

Similarly, “break” and “break into” have different meanings.

My sister broke the glass vase by accident, and immediately broke into tears.