What is a "single"? a "double"? for base ball

How does heroin affect cellular communication in the brain?

According to the article, when our sleep/wake cycle breaks down, we are at an increased risk for all but which select one: a. respiratory illnesses b. dementia c. diabetes d. heart disease

During weight training, when should you exhale? (hope) a. on the lift b. on the recovery c. before the set d. after the set