In Order to Determine Thresholds for Detection of a Spice,researchers

In order to determine thresholds for detection of a spice,researchers diluted various amounts of the spice in 10 litres of water and determined whether those concentrations could be detected by people with normal taste perception.Participants were always able to detect 5 grams of the spice,and never able to detect 1 gram of the spice.About half of the time,participants could detect 2 grams of the spice,and nearly always detected 3 grams.In this example,what is the absolute threshold for detection of this spice

A)  1 gram
B)  2 grams 
C)  3 grams
D)  5 grams