The answer is a. It is not necessary to read or write English to be able to vote.
The passage aims to secure the voting rights of people regardless of their "ability to read, write, understand, or interpret any matter in the English language", by prohibiting the states to put conditions to people to exercise their right to vote.
The Voting Rights Act of 1965 achieved to overcome legal barriers not only at the state level but also to the local level, in the United States.