A new study finds that blacks on death row

问题：

A new study finds that blacks on death row (1) of killing whites are more likely to be executed than whites who kill minorities. It also concludes that blacks who kill (2) minorities are (3) likely to be executed than blacks who kill whites. For example, there is more than a twofold greater risk that an African-American who killed a white will be executed than a white person who kills a (4) victim. A Hispanic is at least 1.4 (5) more likely to be executed (6) such an offender kills a white.

The researchers of the study believe that there are two (7) explanations.. First, prosecutors often win (8) office if they win well-publicized cases. When a black kills a white, such killings gets more (9) and this idea can be (10) by many famous cases. (11) , the court judges at the state level are often (12) to elections, called retention elections. Retention election or judicial retention within the United States court system, is a periodic process, in which the voter (13) approval or disapproval for the judges presently (14) their position, and a judge can be removed from the position if the (15) of the citizens vote him or her out. Just as the researchers (16) out, death penalty is (17) political.

The findings of the study, in short, show that American justice systems clearly (18) white lives more than those of blacks or Hispanics. The researchers also say their findings (19) serious doubts about (20) that the U.S. criminal justice system is colorblind.

6（）

A.only

B.even

C.if

D.unless