[单选题]铸铁焊接时防止产生白口的措施之一是( )。
A.减慢冷却速度
B.提高冷却速度
C.减少焊缝石墨化元素含量

{{B}} Depression{{/B}}
In bed, you toss and turn, unable to get a good night’s sleep. You feel anxious and worried. There’s plenty to do, but the work piles up because you feel listless and tired. You don’t even want to do anything fun. Friends tell you to "pull yourself together," but you feel helpless and hopeless. You have difficulty concentrating and making decisions. When you look in the mirror, you hate yourself. You are definitely in one of life’s valleys—you are depressed.
Everyone gets the blues once in a while. Emotional lows and highs are a normal part of life. The blues become depression when you feel so sleepy and listless that you can’t function normally in everyday life.
{{B}} Types of Depression{{/B}}
Depression can range from a mild panic to self-destructive or suicidal behavior, It’s important to understand the various types of depression so that you can recognize them.
Depression occurs at