Question

which of the following options is correctly punctuated?
A. the runaway truck which had been parked on a steep hill swerved, and teetered before jumping a curb and slamming into a tree.
B. The runaway truck which had been parked on a steep hill swerved and teetered before jumping a curb and slamming into a tree.
C. the runaway truck, which had been parked on a steep hill, swerved, and teetered before jumping a curb and slamming into a tree.
D. the runaway truck ,which had been parked on a steep hill swerved, and teetered, before jumping a curb and slamming into a tree.

Answer 1

B. The runaway truck which had been parked on a steep hill swerved and teetered before jumping a curb and slamming into a tree.

Answer 2

B is good only if there were some other runaway trucks around. Without commas, you have a restrictive subordinate clause.

To me, we start with
The runaway truck swerved and teetered before jumping a curb.

Now you want to describe the truck, so you say
The runaway truck, which had been parked on a steep hill, swerved and teetered before jumping a curb and slamming into a tree.

Without those commas, you have to ask, "Which runaway truck?"
Answer: The runaway truck which had been parked on a steep hill.

So, I don't like any of the choices: either too many commas, or not enough.

Answer 3

The first two commas in C are correct for the very reasons oobleck gave. This is a perfect example of a nonessential clause, sometimes known as a parenthetical expression.

https://www.englishclub.com/grammar/sentence/parenthetical-expression.htm

I do think, though, that the comma after "swerved" is incorrect -- so that means none of these four choices is right!!

Answer 4

Answer is D