**Core Concept**
Propaganda refers to the intentional dissemination of information, often biased or misleading, to influence people's attitudes, opinions, or behaviors. This concept is crucial in the field of Social and Preventive Medicine, where understanding the dynamics of information dissemination is vital for effective public health interventions.

**Why the Correct Answer is Right**
The correct answer, "Forcing of knowledge into mind," accurately captures the essence of propaganda. Propagandists often use persuasive techniques, such as repetition, emotional appeals, or logical fallacies, to implant their message into the minds of their audience without allowing for critical evaluation or informed consent. This can be achieved through various channels, including media, education, or even social interactions. The underlying mechanism of propaganda relies on the manipulation of information to shape public opinion, often to serve the interests of a particular group or ideology.

**Why Each Wrong Option is Incorrect**
**Option B:** Active acquiring of knowledge is the opposite of propaganda, which involves the forced dissemination of information rather than voluntary learning.
**Option C:** Requiring knowledge after thinking implies a critical and informed approach to knowledge acquisition, which is not characteristic of propaganda.
**Option D:** Training people to use judgment before thinking is a desirable outcome of education and critical thinking, but it is not a definition of propaganda.

**Clinical Pearl / High-Yield Fact**
A key aspect of propaganda is its ability to bypass critical thinking and directly influence people's attitudes and behaviors. This highlights the importance of media literacy and critical thinking skills in evaluating information, especially in the context of public health interventions.

**✓ Correct Answer: A. Forcing of knowledge into mind**