Passage: In the following passage, some words have been deleted. Read the passage carefully and select the most appropriate option to fill in each blank. Friedrich Nietzsche was a German philosopher. He (1)_______ his career as a classical philologist but later turned to philosophy. He (2)_______ the youngest person to hold the Chair of Classical Philology at the University of Basel, (3)_______ resigned in 1879 due to health problems (4)_______ plagued him most of his life. In 1889, he suffered a collapse (5)_______ afterward, a complete loss of his mental faculties. Question: Select the most appropriate option to fill in blank number 2.

1. become
2. became
3. turned
4. are