In order to answer this question, first we need to understand the meaning of the words in options a, b, c and d.

Net capital outflow=(Value of Dollars converted into foreign currency to invest in other countries) ~(Value of Dollars created by converting foreign currency into Dollars for investing in US by foreigners)

Net Exports=(Value of Dollars converted into foreign currency for importing foreign goods) ~(Value of Dollars got from foreigners by exporting)

So, by understanding the above two words we can say that demand for dollars in the market for foeign currency exchange comes from (net exports + net capital outflow). So, the option 'b' is correct.

The imposition of an import quota means restricting the importing amount of goods from foreign nations so that it can reduce the dollars payment to foreign nations and hence it reduces the supply of Dollars in the foreign currency markets.

From the above explanation, we can say that the imposition of an important quota shifts the supply of currency left, so the exchange rate rises.