[单项选择]

One day two scientists were quarrelling about whose watch was better, the German one or the Japanese one. Since they were scientists, they decided to do an experiment to test the watches. They went into their lab and filled a basin with water, put the watches in, waited for 20 minutes and took them out.
They could see there was something wrong with both watches. They observed them for several hours before speaking to each other. They both silently found that the German watch was losing 60 minutes and the Japanese are doubled that.
The scientist with the Japanese watch then slowly raised his head and said, "Both watch are out of work, but my watch is right more often than yours, so it’s better." The scientist with the German watch went home without saying a word.

The two scientists were quarrelling at the beginning of the story, because （　）.
A. the Japanese watch was better
B. the German watch was better
C. each of them thought his own watch was better than the other’s
D. both the watches were wrong