Answer:
a. The Fed intervened in the foreign exchange market and sold dollars.
When the Fed intervenes and supplies dollars in the foreign exchange market, the amount of dollars in the market will rise and the law of supply and demand concludes that when the supply of something increases relative to its demand, it will lose value. The US$ will therefore lose value.
c. People began to expect that the U.S. dollar would depreciate.
If people expect the US$ to depreciate, they will take action to protect themselves from this depreciation by selling off their dollar assets for instance. This would lead to excess dollars in the market which would then lead to the US$ depreciating as explained above.