Answer:
B. Below.
C. On.
B. Across.
Step-by-step explanation:
Prepositions are the parts of speech which provide the location/position of the thing talked about. They are used to connect nouns, pronouns or even phrases with the other people or give the time or location/ place of the other people.
1. The life jackets are stored below the deck.
The preposition here is BELOW which shows the position of the life jackets. It gives the location of the life jackets, making it easy for their easy finding.
2. I hope to visit my Grandmother on Wednesday.
Here, the preposition is ON for it tells the time/exact day of the speaker's plan to visit his/ her grandmother. It provides the extended detail for the visit, giving a specific detail.
3. If you walk across the bridge, you will see two windmills.
Lastly, the preposition in this sentence is ACROSS which suggest/ shows the very act of moving. It is usually followed by a noun, in this case "the bridge".