A string of length 0.4 m and mass \[{{10}^{-2}}\,kg\] is tightly clamped at its ends. The tension in the string is 1.6 N. Identical wave pulses are produced at one end at equal intervals of time Dt. The minimum value of Dt which allows constructive interference between successive pulses is [IIT 1998]

• A.            0.05 s                                       
• B.            0.10 s
• C.            0.20 s                                       
• D.            0.40 s