What is a taste threshold test?

The basic tastes of sweet, salty and sour have different thresholds, or concentration levels, at which they can be detected. In other words, it is easier to detect some flavors at low concentrations compared with other flavors. Taste thresholds can vary from person to person.

where's the diagram?

the positions which points up in upward carbon and down in downward carbon are axial

and vice versa holds true for equatorial positions

so the correct answer with labelled diagram will be