Explanation:
The correct preposition to use in this sentence is "in".

When we say "walked along silence," we mean that we walked while there was silence around us. The word "along" is used to indicate movement or progression in a particular direction. In this case, it suggests that we were moving or progressing in the presence of silence.

Let's look at the other options and why they are not suitable in this context:

a) In: This is the correct preposition because it indicates movement or progression within the presence of silence.

b) In spite of: This preposition is not suitable in this context because it suggests that there is some form of opposition or contradiction between walking and silence. However, in this sentence, we are simply describing the act of walking while there is silence around us.

c) Without: This preposition suggests an absence or lack of something. If we say "walked without silence," it implies that there was noise or sound while walking. However, the sentence is specifically describing walking in the presence of silence.

d) For the sake of: This preposition is not suitable in this context because it suggests that the purpose or motive for walking is silence. However, the sentence is simply describing walking while there is silence around us, without any specific purpose or motive related to the silence.

In conclusion, the correct preposition to use in the given sentence is "in" because it accurately conveys the meaning of walking while there is silence present.