Which of the following is an example of an ineffective thesis statement?

A. Students can attain success in the online classroom through dedication, accountability, and effective time management.
B. The problem of pollution in major cities can be alleviated by limiting the number of cars on the street, creating more efficient public transportation systems, and planting more trees.
C. You can be successful in an online class if you just put your mind to it.
D. Long term drug use can have serious negative effects on one's marriage, career, and health.