Pick from:
[1]. aerobic capacity
[2]. relaxation of muscles
[3]. the looseness of soil
[4]. sunlight
[5]. air
[6]. metabolic reaction
[7]. blood
[8]. Converting waste.
Q: Fact 1: Urine leaves the body through a sphincter in the process of urination. Fact 2: Urination requires relaxation of the sphincter muscle. Given the two facts above, what does the process of urination require?
A:
[2].