A second harmonic has to be generated in a string of length l stretched between two rigid supports. The point where the string has to be plucked and touched are

• A

  Plucked at $\frac{\mathrm{l}}{4}$ and touch at $\frac{\mathrm{l}}{2}$

• B

  $\mathrm{plucked} \mathrm{at} \frac{\mathrm{l}}{4} \mathrm{and} \mathrm{touch} \mathrm{at} \frac{3\mathrm{l}}{4}$

• C

  $\mathrm{plucked} \mathrm{at} \frac{\mathrm{l}}{2} \mathrm{and} \mathrm{touched} \mathrm{at} \frac{\mathrm{l}}{4}$

• D

  $\mathrm{Plucked} \mathrm{at} \frac{\mathrm{l}}{2} \mathrm{and} \mathrm{touched} \mathrm{at} \frac{3\mathrm{l}}{4}$