Answer:
C) high foreign saving rates.
Step-by-step explanation:
US savings rate is approximately 8.8% (2018 data) while some countries like Japan have an average savings rate of over 28%, China's and Singapore's savings rate are above 40%, European countries like Switzerland, Luxembourg, or Sweden have savings rates of approximately 16-18%. On average, countries that belong to the European Union have an average savings rate of approximately 12%.
That means that other developed countries have a much higher savings rate than the US, therefore they have excess amount of funds. An important percentage of those excess funds are invested in the US.