Answer: D. Nuclear Membrane breaks down
Explanation: 
- During prophase, duplicated chromosomes condense, shorten, and thicken
 - Homologous chromosomes come together and form pairs. This is called synapsis. Crossing over takes place
 - The membrane around the nucleus breaks apart and the nucleolus disappears
 
Also, the nuclear membrane needs to break down in order to replicate the parent's chromosomes and make a new cell in the first phase of meiosis.