"You want to test the mutagenicity of a certain chemical that you suspect causes changes to DNA molecules. You have not been able to locate the Salmonella typhimurium strain that requires histidine in order to grow. What might you be able to use instead?"

the ems is the abbreviation for the emergency medical services. it is a service provided by a group of medical professionals specialised doctors and other healthcare staff.

any one can call 911 in case of any medical emergency and a group of health care professional will come and give the treatment required. every day the ems staff receive many phone call, which are related to different types of medical emergencies, out of which 25-28% are exclusively related to the respiratory issues.

so, the correct answer is 25-28%.

answerjudgment and reasoning;