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C is corrent because such testing ordinarily relies upon good internal control existing for the period after the testing. Also, be aware that such "interim" testing is considered inherently more risky.
A is incorrect because first-year audit engagements are ordinarily considered as higher risk than subsequent audits; accordingly, performing such substantive procedures prior to year-end is not ordinarily desirable. 
B is incorrect because a high turnover of senior management may represent a risky situation in which the auditor will wait until year-end to perform most substantive procedures.
D is incorrect because such a new sales incentive program does not have an obvious directional effect on internal control or audit risk.