Topic: Fill in the Blank,

Best Answer Explained in Below-:

The sentence "In today's fast changing world, it is very difficult to ___ what will happen in the future" implies a need for insight or foresight into future events. Among the options provided, the word "predict" (Option B) is the most fitting.

To "predict" means to estimate or forecast a future event based on current knowledge or trends, which aligns perfectly with the context of uncertainty in a rapidly changing environment. The evolution of technology, society, and global dynamics can make future outcomes particularly unpredictable, making the act of prediction inherently challenging.

In contrast, the other options do not hold the same contextual relevance:
- "Present" (Option A) refers to showing or displaying something and does not relate to anticipating future events.
- "Prefix" (Option C) involves placing something in front of another word and has no connection to future forecasting.
- "Pretend" (Option D) means to act as if something is true when it is not, which similarly does not involve making educated forecasts.

Therefore, "predict" is the most appropriate choice, accurately capturing the struggle to foresee what lies ahead in a world characterized by rapid change.