D and B are the answers.
For the first one, the wagons had 2 things that helped them, one is the wheels and the other is the floor So D explains it the proper way.
For the second one, B is the answer. The scientists did 3 things and all three things are in parallel with "ing" form. You need to have "that"(I sometimes get confused as well with the usage of when to use"that" and when "not to", so if someone can throw some light on it, appreciate it)which A omits, so B is the right one. My reasoning for using "that" is, the scientist literally didn't "find the noise", but they foound "that the noise" is continuous.
I would say they are medium ranged questions and both of them were testing little bit of parallelism and modifiers.
Can
and B...wat r d OAs??
