My mother went to the grocery store for buying food for our upcoming camping trip.

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using an infinitive, what is the correct way to replace the underlined words?

a) my mother went to the grocery store to buy food for our upcoming camping trip.
b) my mother went to the grocery store for to buy food for our upcoming camping trip.
c) my mother went to the grocery store to be buying food for our upcoming camping trip.
d) my mother went to the grocery store for to be buying food for our upcoming camping trip.