The figure shows two cases. In the first case,a spring (spring constant $K$) is pulled by two equal and opposite forces $F$ at both ends. In the second case,it is pulled by a force $F$ at one end while the other end is fixed. The extensions $(x)$ in the springs will be:

• A
  In both cases $x = \frac{2F}{K}$
• B
  In both cases $x = \frac{F}{K}$
• C
  In the first case $x = \frac{2F}{K}$,in the second case $x = \frac{F}{K}$
• D
  In the first case $x = \frac{F}{K}$,in the second case $x = \frac{2F}{K}$