Scientific knowledge has its dangers, but so has every great thing. Over and beyond the dangers with which it threatens the present, it opens up as nothing else can, the vision of a possible happy world; a world without poverty, without war, with little illness. Science, whatever unpleasant consequences it may have by the way, is in its very nature a liberator.

Which one of the following is the most important implication of the passage?

The correct option is: A happy world is a dream of science.

Here is a step-by-step breakdown of why this option is the most important implication of the passage:

1. Analyzing the core theme of the passage:
The passage discusses that while scientific knowledge carries risks and dangers, it has a uniquely powerful positive potential. Specifically, the author states that science "opens up as nothing else can, the vision of a possible happy world; a world without poverty, without war, with little illness." This "vision" of a happy world is essentially a dream or aspiration that science enables us to visualize and work towards.

2. Deconstructing the other options:
- "Science only can build a happy world, but it is also the only major threat."
This statement is too extreme. The passage says scientific knowledge "threatens the present" and "opens up as nothing else can, the vision of a possible happy world." However, it does not state that science is the only major threat to the world, nor does it claim science is the sole mechanism that can build it, only that it uniquely opens up the vision.
- "A happy world is not possible without science."
The passage highlights science as a key liberator that shows us the vision of a happy world, but it does not logically establish that a happy world is completely impossible under any other circumstances or without science.
- "A happy world is not at all possible with or without science."
This directly contradicts the tone and message of the passage, which explicitly describes a "possible happy world" visualized through science.

3. Conclusion:
Since science uniquely "opens up... the vision of a possible happy world," it serves as the vehicle for dreaming of and conceptualizing such a world (one free of poverty, war, and illness). Therefore, the implication that "A happy world is a dream of science" best aligns with the passage's description of science presenting us with this grand vision.