Which statement correctly distinguishes continuous-time (CT) signals from discrete-time (DT) signals and provides valid examples?

Which statement correctly distinguishes continuous-time (CT) signals from discrete-time (DT) signals and provides valid examples?

• A. CT signals are defined for all real time t; examples: x(t)=cos(2π f0 t), x(t)=e^{−α t} u(t).
• B. CT signals are defined only at integer times; examples: x(t)=cos(2π f0 t), x(t)=e^{−α t} u(t).
• C. DT signals are defined for all real time t; examples: x[n]=cos(ω0 n).
• D. DT signals are defined only at even integers; examples: x[n]=(1/2)^n u[n].

Answer: (A)