Read the following statements and select the correct option stating which one is true (T) and which one is false (F).
( A ) ABO grouping is based on the presence or absence of two surface antigens on leucocytes.
( B ) During first pregnancy there is least chance of occurrence of erythroblastosis foetalis due to Rh incompatibility.
( C ) During blood clotting, conversion of fibrinogen to fibrin occurs by action of enzyme thrombokinase.
( D ) All chordates prossess chambered, muscular, dorsal heart to pump blood throughout the body.

Options

A. a(T), b(F), c(F), d(T)
B. a(T), b(T), c(F), f(T)
C. a(F), b(T), c(F), d(F)
D. a(F), b(F), c(F), d(T)

Answer

To solve the question, we need to evaluate each statement one by one and determine if they are true (T) or false (F).

### Step-by-Step Solution:

1. **Statement A**: "ABO grouping is based on the presence or absence of two surface antigens on leucocytes."
- **Evaluation**: This statement is **False**. ABO blood grouping is determined by the presence or absence of specific antigens (A and B) on the surface of erythrocytes (red blood cells), not leucocytes (white blood cells).

2. **Statement B**: "During first pregnancy there is least chance of occurrence of erythroblastosis foetalis due to Rh incompatibility."
- **Evaluation**: This statement is **True**. In the first pregnancy, the mother’s immune system has not yet been sensitized to the Rh factor, so the chance of erythroblastosis foetalis (a condition where the mother’s immune system attacks the fetus's red blood cells) is minimal.

3. **Statement C**: "During blood clotting, conversion of fibrinogen to fibrin occurs by action of enzyme thrombokinase."
- **Evaluation**: This statement is **False**. The conversion of fibrinogen to fibrin during blood clotting is catalyzed by the enzyme thrombin, not thrombokinase.

4. **Statement D**: "All chordates possess chambered, muscular, dorsal heart to pump blood throughout the body."
- **Evaluation**: This statement is **False**. While many chordates have a muscular heart, not all have a dorsal heart; some have a ventral heart, and the number of chambers can vary (two, three, or four).

### Summary of Evaluations:
- A: False (F)
- B: True (T)
- C: False (F)
- D: False (F)

### Final Answer:
The correct option stating which one is true (T) and which one is false (F) is:
- A: F
- B: T
- C: F
- D: F