37 Special Drawing Rights (SDR) are
a) an artificial international reserve allotted to the members of the International Monetary Fund (IMF), who can then use it for transactions among themselves or with the IMF.
b) a "portfolio" of currencies, and its value tends to be more stable than the currencies that it is comprised of.
c) used in addition to gold and foreign exchanges, to make international payments.
d) all of the above