What is the best way to combine Sentences 14 and 15? I thought about napkins for a long time I could not come up with something magnificent. I thought about napkins for a long time, and I could not come up with something magnificent. I thought about napkins for a long time, so I could not come up with something magnificent. I thought about napkins for a long time, but I could not come up with something magnificent.

I thought about napkins for a long time, but I could not come up with something magnificent.

Explanation:

1. I thought about napkins for a long time I could not come up with something magnificent Here there is no conjunction  to  enable the two sentence make a contrasting or co-joining  meaning

2.  I thought about napkins for a long time, and I could not come up with something magnificent.

The conjunction AND is not the best way to combine the two sentences. "and" in sentences is used to connect two actions, with one following the other.

3. I thought about napkins for a long time, so I could not come up with something magnificent

So is used as a  subordinating conjunction used to express reason for an action and therefore cannot be applied here.

4. I thought about napkins for a long time, but I could not come up with something magnificent.

The best way to combine the sentences is the use of but which is used here to express a contrast( difference ) in an action

a) madame podtochina used witchcraft to make it disappear.

sorry, idk never read it