Explanation:

- I. Nature of litigation: This factor helps determine the complexities involved in the case, which influences the number of witnesses needed.

- II. Number of the issues required to be proved: More issues may require more witnesses to provide adequate evidence for each point.

- III. Nature of the issues: Complex or technical issues might require expert witnesses, increasing the number involved.

- IV. The fact as to on whom the onus has been laid: Knowing who has the burden of proof can influence the number of witnesses presented.

- V. The specified purpose for which a particular witness is required to be produced: Specific witnesses may be needed for certain aspects, affecting the total number.

Option 4: All of these -

All the guidelines listed are relevant in determining the number of witnesses in court.