1. the sussex pledge to stop attacks on unarmed ships.
2. the sinking of the lusitania by germany
3. the us declares war on germany
4. germany announces the resumption of unrestricted submarine warfare.

arrange these items in correct chronological order.

a. 1,2,3,4
b. 1,2,4,3
c. 1,4,3,2
d. 2,1,4,3