Which of the following is usually referred to as 'black gold' ?

Options

A. coke
B. coal tar
C. petroleum
D. coal

Answer

To solve the question "Which of the following is usually referred to as 'black gold'?", we can follow these steps:

### Step 1: Understand the term 'black gold'
- The term 'black gold' is often used to refer to a substance that is valuable and has a black color.

### Step 2: Identify the options
- While the question does not provide specific options, we can infer that common substances referred to as 'black gold' include petroleum and coal.

### Step 3: Analyze the characteristics of petroleum
- Petroleum is a black liquid when extracted in its crude form. It is a valuable resource used in the production of various products such as gasoline, plastics, and pharmaceuticals.

### Step 4: Compare with other substances
- Although coal is also a valuable resource, it is not commonly referred to as 'black gold'. The term is predominantly associated with petroleum due to its economic importance and wide range of applications.

### Step 5: Conclude the answer
- Based on the analysis, the substance that is usually referred to as 'black gold' is petroleum.

### Final Answer:
Petroleum is usually referred to as 'black gold'.

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