The reason A is the answer is that borrowing from overseas will cause an increase in foreign debt, printing money wil increase inflation and selling assets is a one off venture so this is not included in the fiscal outcome. Hence, A is the best mechanism to finance a budget.
That tends to be a problem with domestic borrowing, however it's affected by global economic conditions. For example, during a trough in the business cycle the government is less likely to crowd out the pricate sector as investment and spending would be low at this time. However, if a government continued to borrow even in periods of high economic growth then the 'crowding out' effect may occur.