The correct answer to this open question is the following.
Although there are no options attached we can say the following.
Blacks were worried about the progress of the civil rights movement under the new leadership of President Johnson because, after the assassination of President John F. Kennedy, they believed that the Civil Rights Act could be delayed or forgotten. Some blacks thought that one of the motives of the assassination could have been President Kennedy's support of the Civil Rights Act. Furthermore, in US Congress, Republicans and Democrats had expressed criticism and opposition to the passing of that act.
Indeed, blacks were afraid of the strong opposition to the act by Southern Congressmen. It was a difficult and tense time, but finally, new US President Lyndon B. Johnson signed the Act into law on July 2, 1964.