A heat engine absorbs heat $Q_1$ at temperature $T_1$ and heat $Q_2$ at temperature $T_2$. Work done by the engine is $\left(Q_1+Q_2\right)$. This data

First law: Energy can neither be created nor be destroyed. It can be transformed from one form to another form

Given that the total amount of energy absorbed by the system at temperatures $T_1$ and $T_2$ is $\left(Q_1+Q_2\right)$

The work done by the engine is $=\left(Q_1+Q_2\right)$

Here heat absorbed is converted to work

Hence the correct option is (D).