Before we look at the answer choices, let's first consider which topics the given sentences discuss. After all, the sentences can't easily support inferences that are about topics they don't talk about! The first sentence is from the section "A Type of Fossil." It's talking about how most fossils are imprints of ancient creatures or only partial remains of their bodies, such as their skeletons. The second sentence is from the section "From Tree to Stone." It is talking about how for petrification to occur, a tree has to be buried so that oxygen cannot get to it, oxygen being the cause of rotting.

Now that we've reviewed these sentences closely, let's look at each of the answer choices and figure out which inference the sentences support.

"The bark and wood of a petrifying tree preserve the tree’s interior by blocking its exposure to oxygen." - This isn't true at all; the second sentence says that during petrification, oxygen cannot get to a tree's bark and wood. The second sentence contradicts this statement directly, so this statement can't be the correct answer.

"Most fossils involve bodies of creatures that are completely preserved from rotting." - The sentences don't support this answer choice. The first sentence tells us that "most fossils" are only partial remains of creatures or imprints they made, which is at odds with this answer choice. Since it's contradicted by the first sentence, it can't be correct.

"Oxygen probably helped preserve the footprints of dinosaurs as fossils." - This answer choice discusses both oxygen (mentioned in the second sentence) and footprints (mentioned in the first sentence); however, it suggests that oxygen helps preserve the footprints. We're told that oxygen causes things to rot, but we're not told anything that would support the claim that it helps preserve footprints. This answer choice isn't correct either.

"Mineral-containing water must have gotten to the dinosaur bones and turned them to stone." - Neither of the sentences mention water at all, much less mineral-containing water, so this claim isn't supported by them.

"The bodies of dinosaurs whose bones became fossils were probably exposed to oxygen." - This is the correct answer. In the second sentence, we're told that oxygen is the cause of making trees rot. In the first sentence, we're told that some fossils are just the bones of dinosaurs, not the rest of their bodies. Putting these two concepts together, we can arrive at the conclusion that the bodies of the dinosaurs whose skeletons became fossils probably rotted away due to contact with oxygen.

We can find the answer to this question by looking at the text. Based on the text, Jo thought she should buy her mother a Christmas gift because her father told her to take care of their mother when he left. 

They are quite worn out; Marmee must have a new pair."

"I thought I'd get her some with my dollar," said Beth.

"No, I shall!" cried Amy.

"I'm the oldest," began Meg, but Jo cut in with a decided—

"I'm the man of the family now papa is away, and I shall provide the slippers, for he told me to take special care of mother while he was gone."