Fact 1: Viruses cannot reproduce by themselves.

Fact 2: Viruses attach themselves to cells and reproduce.

Given the two facts above, answer the question "How can viruses make copies of themselves?" with the following options: 
- A compound that donates proton
 - attach themselves to cells
 - have sex with another virus
 - distances themselves from cell
 - attach themselves to viruses
 - it needs them
 - rapid expansion
 - By wind and rain


 

  attach themselves to cells       