When a certain string is clamped at both ends, the lowest four resonant frequencies are $50,100,150,$ and $200$ Hz When the string is also clamped at its midpoint, the lowest four resonant frequencies are:

$25,5075,$ and $100$ Hz

$50,100,150,$ and $200$ Hz

$50,150,250,$ and $300$ Hz

$75,150,225,$ and $300$ Hz

$100,200,300,$ and $400$ Hz