In the following passage, some of the words have been left out. Read the passage carefully and select the correct answer for the given blank out of the four alternatives.

The English language is ___________ complex in character that it can scarcely be learned by rule, and can __________ be mastered by the study of such idioms and phrases as are provided in this book; but just as care must be taken to place every accent or stress _________ the proper syllable in the ______________ of every word it contains, so must the stress or emphasis be placed on the proper word in ___________ sentence spoken.