DSE 2021 Question 43: Linear regression and OLS

You have three variables $Y, X_1, X_2$. First you regress (OLS) $Y$ on $X_1$ and $X_2$ to get the regression coefficients corresponding to $X_1$ and $X_2$ as $b_1$ and $b_2$ respectively. Then you also regress (OLS) $Y$ on $X_1$ and $X_1 + X_2$ to get the coefficients corresponding to $X_1$ and $X_1 + X_2$ as $c_1$ and $c_2$ respectively. Which of the following statements is correct?