To complete the crossword puzzle with 'O' and fill each gap in the sentences, let's first look at the clues for the crossword.

Given the crossword structure:
1. O _ _
2. O _
3. O _ _
4. O _ _
5. O _ _ _

Here are words that could fit:

1. OVEN
2. OPAL
3. OMOS
4. OXEN
5. OVAL

Now, for filling in the sentences, let's assume some common examples:

1. The **oven** is preheated to bake the cake.
2. She wore an **opal** ring that sparkled beautifully.
3. The **omos** in the kitchen are used for various tasks.
4. The farmer raised **oxen** for heavy work in the fields.
5. The picture was framed in an **oval** shape.

Adjust the sentences according to the specific context you're working with, but these examples should give you a good starting point!