Final answer:
Alterations to building ventilation systems are an indicator of a meth lab, as are excessive trash, the presence of cyanides or acids, and shrapnel-type materials due to dangerous chemical use and by-product disposal. Option A is correct.
Step-by-step explanation:
Among the indicators of a meth lab, alterations to building ventilation systems can be a sign. Meth production often involves the use of volatile and toxic chemicals that create dangerous fumes. To manage these fumes, producers may modify ventilation systems. Therefore, the presence of abnormal or makeshift ventilation could indicate the presence of a meth lab.
Additionally, excessive trash could be found due to discarding of chemical containers and by-products, cyanides or acids could be present as they are often used in meth production, and shrapnel-type materials might be a result of makeshift reactions leading to explosions or contamination.