The use of the silk roads decreased when

The use of the Silk Road decrease began as early as the Song Dynasty, and this decrease was fueled by the rise in Chinese maritime trade and the high customs duties required by the Arabs. Consequently, new trade centers in Southeast Asia emerged.

Explanation:

There was no danger of long inland voyages and costs for brokers on maritime voyages. With the rise of the expansion of European naval forces at the beginning of a new era, the Silk Road is finally losing its meaning. The trade in silk is replaced by ships, with Chinese traders making their way to India and Arabia. Since the Song Dynasty, Europeans have been very restricted in trading with China. At the time of naval expansion, one of the main goals was to rediscover the sea route to fairytale China (China).

A) The government could not issue more currency than it had gold.  

As the U.S. was coming to an economic crisis, by 1929 people didn't trust any financial institution anymore and the atmosphere was filled with high speculations about the value of the American currency and other nations' in the near future. As a result, people began to hoard more gold, the strongest asset, its demand increased sharply as well as its prince, and the government could not issue more currency than it had gold.