Choose the word(s) CLOSEST in meaning to the underlined word(s): Birds are at their most vulnerable when they leave their nests an

Question:

Choose the word(s) CLOSEST in meaning to the underlined word(s): Birds are at their most vulnerable when they leave their nests and find food on their own.

• 
  A.
  strong
• 
  B.
  susceptible
• 
  C.
  powerful
• 
  D.
  invincible