Which of the following is true about myoglobin?

A. This appears slowly after myocardial necrosis but has not achieved widespread use in cardiac practice.

B. Myoglobin can only be found in muscle tissue and would be present in the bloodstream if there is damaged muscle tissue.

C. Rises in the first 30 minutes and slowly excreted from the kidneys.

D. Since it has no specificity, positive values are important rather than negative values.