A. Although the serf's lot is in any case a hard one, it is apt to be rendered more harder by one or both of two enemies: the money lender and the land owner.
B. It is only a base camp from which dangerous climb can begin.
C. We now know that limelight and a brass band do more to persuade than can be done by the most elegant train of syllogisms.
D. Soil and raw materials must not be used up so fast that scientific progress cannot continually make good the loss by means of new inventions and discovering.
E. The real and present difficulty will be to reach an financial paradise without a previous success in limiting population.
In statement A, the use of the term "more harder” is wrong, as the comparative word is 'harder', or 'more hard'.
In statement E, since the statement reads- The real and present difficulty, hence the verb that follows should be in the present tense 'is to reach' and not "will be to reach” as that is in the future tense.
Hence, the correct answer is option AE.