The gaseous reaction $A+ B\rightleftharpoons 2C+D +q kJ,$ is most favored at:

Low temperature has no effect since the balance shifts to the products and more heat is produced as a result. Low pressure causes the reaction to change its direction, producing more and more products as a result of which the total moles and pressure rise. Low pressure is therefore rendered useless.

Therefore, the correct answer is option (B) Low temperature and low pressure.