<qa>  How many different dose levels of AMG 531 are being studied?Participants in Arm B will receive either AMG 531 or placebo on Day 5 and 7. Every 2 out of 3 participants in Arm B will receive AMG 531. One out of every 3 participants in Arm B will receive placebo. The dose of AMG 531 that participants in both Arms A and B receive will depend on when they enroll on the study. There are 3 different dose levels of AMG 531 being studied. Each new group of participants will receive a higher dose than the previous group. 