Could be false. It is possible that cream that has been whipped ineffectively can become a substance that is not thick and velvety. We know that cream whipped in a blender becomes thick and velvety, but perhaps other methods of whipping can produce something ineffective that isn't thick and velvety.

Must be true. The stimulus tells that although this special attachment can help, the attachment cannot fully compensate for the container’s lack of air intake. Therefore, the special attachment is not enough by itself to whip cream completely effectively.

Could be false. To claim that the attachment always produces a fluffier result is too extreme. The stimulus tells us that the attachment can help somewhat, but we don't know whether this means the attachment always produces fluffier results.

Could be false. We don’t have any information in the stimulus that suggests how the attachment functions. It might work by reducing the total amount of air required to whip cream effectively, but it might also work by letting more air in.

Could be false. We don't know what is or is not the most common way to produce whipped cream. Nothing in the stimulus relates to the popularity of a whipping method.