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Tubes Matched Pair

Tubes Matched Pair
Statistics homework help please!?

Is "tartar control" Crest toothpaste more effective at preventing tartar build-up on teeth than regular Crest toothpaste? Researchers recruit 200 volunteers (109 men and 91 women) who first get a free tooth cleaning. Then the researchers randomly assign 100 to the tartar control group and 100 to the regular toothpaste group. All 200 people are given unmarked tubes of the appropriate toothpaste and instructed on how often to brush their teeth each day. They are not told which group they are in, and the two kinds of toothpaste look the same. After 6 months, they are rated on tartar build-up by dentists who don't know who was in each group.
This is an example of:
a: matched-pairs of designs.
b: a completely randomized design.
c: a block design.
d: more than one of the above.
e: none of the above.

b. It's a randomized design. You're not matching here, nor blocking (segregating the participants into subgroups).