The resonance phenomena occurs when the system:

Options

A. Oscillates at a certain frequency
B. Have Rand L only
C. Have L and C
D. Both (a) and (c )

Explanation

To solve the question regarding the resonance phenomena in a system, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Resonance**: Resonance occurs in a system when the frequency of the external force matches the natural frequency of the system. In electrical circuits, this typically involves inductors (L) and capacitors (C).

2. **Impedance in AC Circuits**: The impedance (Z) in an RLC circuit is given by the formula:
\[ Z = \sqrt{R^2 + (X_L - X_C)^2} \]
where \(X_L\) is the inductive reactance and \(X_C\) is the capacitive reactance.

3. **Condition for Maximum Current**: The current in the circuit is given by:
\[ I = \frac{V}{Z} \]
For the current to be maximum, the impedance (Z) must be minimum.

4. **Minimizing Impedance**: The impedance will be minimized when the term \((X_L - X_C)\) is zero. This occurs when:
\[ X_L = X_C \]

5. **Reactance Equations**: The inductive reactance \(X_L\) is given by:
\[ X_L = 2\pi f L \]
and the capacitive reactance \(X_C\) is given by:
\[ X_C = \frac{1}{2\pi f C} \]
Setting these equal gives:
\[ 2\pi f L = \frac{1}{2\pi f C} \]

6. **Solving for Resonant Frequency**: Rearranging the above equation leads to:
\[ (2\pi f)^2 = \frac{1}{LC} \]
Therefore, the resonant frequency \(f\) is:
\[ f = \frac{1}{2\pi \sqrt{LC}} \]

7. **Conclusion**: The resonance phenomenon occurs when the inductive reactance equals the capacitive reactance in a circuit containing inductors and capacitors, allowing the current to reach its maximum.

### Final Answer:
The resonance phenomena occurs in a system when the inductive reactance \(X_L\) equals the capacitive reactance \(X_C\).