Step 1: Understanding the Texts.
Das Kapital, written by Karl Marx, is often referred to as the 'Bible of Socialists'. It is a foundational text for understanding the economic theory behind socialism. While the Communist Manifesto is also highly influential, Das Kapital goes into more depth on Marxist theory.
Step 2: Analysis of options.
- (A) Communist Manifesto: Although a critical work by Karl Marx, it is not commonly called the 'Bible of Socialists'.
- (B) April Theses: This is a work by Lenin, but not referred to as the 'Bible of Socialists'.
- (C) Das Kapital: Correct, this is often referred to as the 'Bible of Socialists'.
- (D) All of these: Incorrect, while all these works are important, Das Kapital is the most common text associated with this title.
Step 3: Conclusion.
The correct answer is (C) Das Kapital.