In which one of the following do the two names refer to the same thing?

The correct option is A

Tricarboxylic acid cycle and Citric acid cycle

The correct option is A.

Explanation for correct option:

1. The tricarboxylic acid cycle (TCA) and citric acid cycle are also referred to as Kreb's cycle.
2. Since citric acid is the first product of the cycle, that is produced by the condensation of acetyl CoA and OAA(oxaloacetic acid) thus named the citric acid cycle. The Calvin cycle is the process by which carbon fixation is done to produce carbohydrates during photosynthesis.

Explanation for incorrect options:

Option B:

1. The Calvin cycle is the process by which carbon fixation is done to produce carbohydrates during photosynthesis.
2. The tricarboxylic acid cycle (TCA) and Citric acid cycle are also referred to as Kreb's cycle.

Option C:

1. Citric acid is a tricarboxylic acid hence it is also referred to as the tricarboxylic acid cycle.
2. The urea cycle occurs in the liver, in which urea is produced from ammonia.

Option D:

1. Since citric acid is the first product of the cycle, that is produced by the condensation of acetyl CoA and OAA(oxaloacetic acid) thus named the citric acid cycle
2. The Calvin cycle is the process by which carbon fixation is done to produce carbohydrates during photosynthesis.

Final answer: Tricarboxylic acid cycle and citric acid cycle refers to the same thing.