B is corrent because by tracing bills of lading to sales invoices, the auditor obtains evidence that merchandise which has been shipped (as evidenced by a bill of lading) has been invoiced. A is incorrect because the sales invoices do not provide sufficient evidence that the sale was recorded. C is incorrect because to determine whether invoiced sales were shipped the auditor would trace from sales invoices to bills of lading (the opposite of this question). D is incorrect because to determine whether recorded sales were shipped the auditor would trace from the population of recorded sales in the sales journal to bills of lading.
