Which of the following cannot be the probability of an event?

Options

A. 0.7
B. `(2)/(3)`
C. `-1.5`
D. 0.15

Answer

To determine which of the given options cannot be the probability of an event, we need to understand the fundamental properties of probability.

### Step-by-Step Solution:

1. **Understanding Probability**:
The probability of an event is defined as the ratio of the number of favorable outcomes to the total number of outcomes. Mathematically, it is expressed as:
\[ P(E) = \frac{\text{Number of Favorable Outcomes}}{\text{Total Number of Outcomes}} \]

2. **Range of Probability**:
The value of probability must always lie between 0 and 1, inclusive. This means:
\[ 0 \leq P(E) \leq 1 \]
- A probability of 0 means the event cannot happen.
- A probability of 1 means the event is certain to happen.

3. **Evaluating the Options**:
Let's evaluate the given options based on the range of probability:
- **Option A: 0.7**
- This is between 0 and 1. Therefore, it is a valid probability.
- **Option B: \( \frac{2}{3} \)**
- This is approximately 0.67, which is also between 0 and 1. Thus, it is a valid probability.
- **Option C: -1.5**
- This is less than 0. Therefore, it cannot be a probability.
- **Option D: 0.15**
- This is between 0 and 1. Hence, it is a valid probability.

4. **Conclusion**:
The only option that cannot be a probability of an event is **Option C: -1.5**.

### Final Answer:
**Option C: -1.5 cannot be the probability of an event.**