The coordinates of moving particle at any time t are given by\[x=a{{t}^{2}}\] and\[\text{y }=\text{ b}{{\text{t}}^{\text{2}}}\]. The speed of the particle is

• A.  \[2t(a+b)\]
• B.  \[2t\sqrt{{{a}^{2}}+{{b}^{2}}}\]  
• C.  \[2t\left( \sqrt{{{a}^{2}}-{{b}^{2}}} \right)-2t\left( \sqrt{{{a}^{2}}-{{b}^{2}}} \right)\]
• D.  \[\sqrt{{{a}^{2}}+{{b}^{2}}}\]