A. foreign exchange reserves are substitutes for the base currency.

B.the more international reserves, the better.

There is a substitution relationship between secondary reserves and high-yield reserves in C portfolio investment.

D. commercial principles such as obtaining reasonable income are included in the management principles of official reserves.

E. the opportunity cost of international reserves is the price of giving up buying goods and services with reserves.

Correct answer: d.e.

Answer analysis: A is obviously wrong and ruled out.

Holding reserves also requires a corresponding price. This is manifested in giving up the opportunity to buy goods and services with reserves in the process of holding reserves, that is, the opportunity cost of reserves (e is correct). Therefore, the management of international reserves is particularly important.

A country should have enough primary reserves to meet the trading needs of international reserves, and the remaining reserve assets can be invested in the combination of various secondary reserves and high-yield reserves (C error). In order to obtain the highest possible expected rate of return while maintaining a certain liquidity.

In addition, the commercial principles of managing liquidity risk, market risk, credit risk and obtaining reasonable income have also entered the management principle of official reserves for the first time (D is correct). This means that it is a basic principle of international reserve management to actively manage foreign exchange reserves and maximize profits, and the investment strategy of international reserves is more to pursue high-yield medium-and long-term investment.

Country A should comprehensively weigh the benefits and costs of holding foreign exchange reserves and maintain an appropriate scale of foreign exchange reserves (B error).