The co-efficient of thermal expansion of a rod is temperature dependent and is given by the formula `alpha = aT`, where `a` is a positive constant at T `"in"^(@)C`. if the length of the rod is l at temperature `0^(@)C`, then the temperature at which the length will be `2l` is
A. `sqrt((1n2)/alpha)`
B. `sqrt((1n4)/alpha)`
C. `1/(alpha)`
D. `2/alpha`