Which of the following function(s) is/are even ?

Options

1. A$f(x) = \int_0^x \ln(t + \sqrt{1 + t^2}) dt$
2. B$g(x) = \int_0^x \frac{(2^t + 1)t}{2^t - 1} dt$
3. C$h(x) = \int_0^x (\sqrt{1 + t + t^2} - \sqrt{1 - t + t^2}) dt$
4. D$l(x) = \int_0^x \ln \left( \frac{1 - t}{1 + t} \right) dt$