Question Statement:
When blending biodiesel with conventional diesel fuel up to $20\%$ by volume (B20 blend) in modern tractor CI engines, which of the following modifications is strictly mandatory?
Options:
- (A) Complete redesign and enlargement of engine combustion chambers
- (B) Replacement of natural rubber fuel hoses and seals with synthetic fluoropolymer materials (such as Viton) if degradation occurs
- (C) Installation of an external spark ignition coil and distributor
- (D) Pre-heating fuel to $150^\circ\text{C}$ before entry into the fuel injection pump