题目内容：
根据以下资料，回答题： Karen Rusa was a 30-year-old woman and the mother of four children．For the past several months Karen had been experiencing repetitive thoughts that centered around her children’s safety．She frequently found herself imagining that a serious accident had occurred；she was unable to put these thoughts out of her mind．
On one such occasion she imagined that her son，Alan，had broken his leg playing football at school．There was no reason to believe that an accident had occurred，but she kept thinking about the possibility until she finally called the school to see if Alan was all right．Even after receiving their assurance that he had not been hurt，she described herself as being somewhat surprised when he later arrived home unharmed。Karen also noted that her daily routine was seriously hampered by an extensive series of counting work that she performed throughout each day．Specific numbers had come to have a special meaning to her；she found that her ;she preoccupa-tion with these numbers was hampering her ability to perform everyday activities．
One example was grocery shopping．Karen believed that if she selected the first item on the shelf，something terrible would happen to her oldest child．If she selected the second item，some unknown disaster would fall on her second child．and so on for the four children．Karen’s preoccupation with numbers ex—tended to other activities，most notable the pattern in which she smoked cigarettes and drank cof-fee．If she had one cigarette；she believed that she had to smoke at least four in a row，or one of her children would be harmed in some way．If she drank one cup of coffee，she felt compelled to drink four．Karen acknowledged the unreasonableness of these rules，but，nevertheless，maintained that she felt more comfortable．When she observed them earnestly．when she was occasionally in too great a hurry to observe these rules，she experienced considerable anxiety，in the form of a sub—jective feeling of dread and fear．She described herself as tense，uneasy，and unable to relax during these periods．The occurrence of rarely minor accidents does not reduce her belief that she had been directly responsible because of her inability to observe the rules about number．
The main idea of this passage is to_____． A．describe a woman who suffered from a psychological disease
B．warn the readers against any imagination
C．explain the reason why Karen had such fanciful thoughts
D．present a case for the readers to study
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