You are interested in researching the effects of vitamin c on colds. for your study, you round up a group of people, all roughly the same age and healthy. you give them all vitamin c pills to take every day and have them check in with you once a month to see if they get a cold. why is this not a good study design

the research study lacked a control group, It was  difficult to know individuals who are not taking  Vitamin C and exposed to cold

Explanation:

Normally in a research study there should  be a control group of the same age group like the study group in the same environment, who will not  Vit, C but a   placebo. To determine if Vitamin. C is   the  actual effective drug for prevention of cold  in the study group or other factors.

Therefore, in this study It was  difficult to know individuals who were not taking  Vitamin C and exposed to cold(control group) Because, it is the comparison of the  data from the control  group and the study groups  that is  needed to determine the efficacy of Vitamin C

i think that d. wind is the answer.   i missed the question when i answered a. currents.

affects the water bodies: excessive use of fertilizers causes eutrophication. the fertilizers which are used on plants affect the quality of land on which it is used, further causing erosion of soil. the fertilizers used on plants contain harmful chemical fumes which affect the environment.