Explanation:
The DC load line is a graphical representation of the output characteristics of an amplifier circuit. It is used to determine the operating point or Q-point of the amplifier. The Q-point represents the biasing condition of the amplifier and determines its linearity and efficiency of operation.

A. Contains the Q-point:
The Q-point is the intersection of the load line with the transfer characteristics curve of the amplifier. It represents the voltage and current values at which the amplifier operates under normal conditions. The load line helps in determining the appropriate biasing conditions to ensure the amplifier operates within its linear range.

D. Has a negative slope:
The DC load line has a negative slope because it represents the relationship between the voltage and current at the output of the amplifier. As the load resistance increases, the current flowing through the load decreases, resulting in a decrease in output voltage. This negative slope indicates that as the load resistance increases, the output voltage decreases.

Curvature of the DC load line:
The curvature of the DC load line depends on the characteristics of the amplifier circuit. It can have either a concave or convex shape. The curvature is determined by the non-linearities present in the amplifier circuit, such as the presence of feedback or saturation effects. The curvature affects the linearity of the amplifier and can introduce distortion in the output signal.

Conclusion:
In summary, the DC load line of an amplifier circuit contains the Q-point, which represents the operating conditions of the amplifier. It has a negative slope, indicating the relationship between output voltage and current. The curvature of the load line depends on the non-linearities present in the amplifier circuit.