Reference: IIA Business Knowledge for Internal Auditing, Analytical Procedures section.

Comprehensive and Detailed In-Depth Explanation:
Transfer pricing refers to the pricing of goods, services, and intangibles transferred between related entities. In international transactions, companies often adjust transfer prices to minimize tax liabilities and import tariffs.
Decreasing the transfer price (Option A) results in a lower declared customs value, reducing import tariffs paid to the foreign country.
Increasing the transfer price (Option B) would raise import tariffs, making it less favorable.
Charging the arm's length price (Option C) ensures compliance with tax regulations but does not necessarily reduce import tariffs.
Optimal transfer pricing (Option D) is a general term that does not specifically focus on reducing tariffs.
Thus, decreasing the transfer price is the best approach.
Reference: IIA Business Acumen - Transfer Pricing Strategies