A Researcher Tests the Hypothesis That Large,daily Doses of Vitamin

A researcher tests the hypothesis that large,daily doses of vitamin C help protect against catching the common cold.What would be the best experimental and control group to test this hypothesis?

A) Experimental group: takes a large dose of vitamin C daily;
Control group: takes nothing
B) Experimental group: people with a cold are administered vitamin C daily;
Control group: people without a cold are not administered vitamin C
C) Experimental group: takes a large dose of vitamin C daily;
Control group: takes a large weekly dose of vitamin C
D) Experimental group: takes a large,daily dose of vitamin C;