Critical Reasoning

A new weight-loss drug causes the loss of body fat in all patients who take the drug. In those same subjects, however, the drug also causes the loss of moderate quantities of lean body mass, where "lean body mass" refers to all body mass other than body fat.

Which of the following statements can be properly inferred from the information in the passage above?

Patients taking the new weight-loss drug will not necessarily experience a decrease in their overall percentage of body fat.

The body weight of patients taking the new weight-loss drug will not necessarily decrease.

The new weight-loss drug contains no chemical that exclusively targets the body's fat cells.

Users of the new weight-loss drug should exercise in order to maintain their current levels of lean body mass.

The new drug catalyzes the loss of body fat and the loss of lean body mass via similar mechanisms

[spoiler]OA A

how do we negate C ?? The stat says that lean body mass is lost by the drug so the drug is not necessarily targeting only fat cells.. and attacking muscle tissues too ? A also fits the answer but C fits well too. Do I take this as a poorly constructed question ?
MGMAT CR's sometimes irritate me :/[/spoiler]