Make it the first object to be able to fix and hold your attention upon your studies. He who can do this has mastered many and he who cannot do this will in vain look for success in any department of study.The writer tells us that_______.
选项：

A:if we want to be masters, we must first have an object;
B:if we can't overcome great difficulties, we can't be successful;
C:there are many different ways to achieve success;
D:if we want to be successful, we must concentrate our mind upon our studies