It would be a most unusual way of expressing things.
It's people/passengers/travellers/individuals who ride up and down in buses rather than the buses themselves that ride.
Cars and buses conventionally travel/drive/hurry/move/pass (and many more) up and down.
However, it would not be unusual, after test driving a vehicle with heavy suspension or steering,...
It depends entirely on the requirements of the particular head-word (which are unpredictable, and just have to be learnt).
Afraid can take an "of" phrase (consisting of "of" + noun phrase), or it can take a "that" clause. but "of" cannot take a "that" clause. So your second example is grammatical, but your first is not. (I am afraid of the possibility that ...
Grammatically speaking - the verb needs a subject.
What Java object type would you abstract the number of apples to?
Alternatively you can put it in the passive voice:
What Java object type would the number of apples be abstracted to?
On more of a technical level, I probably wouldn't use abstract for assigning a simple count of the number of objects, ...
It's a matter of perspective. When you use was, you're looking back on the trip. When you use has been, you're looking at the trip from the present.
Suppose you're talking to someone about a trip you took to Europe last year. You'd say:
It was a nice trip.
Now suppose it's the last day of your trip to Europe, and you're talking to your travel partner:...