问题详情

According to the passage, the absolute brightness of a Cepheid variable______.
A．depends upon its measurable distance from an observer on earth
B．may be determined from the length of its cycle of variation
C．changes from time to time according to a regular and predictable pattern
D．indicates the strength of the gravitation force exerted by the star此题为多项选择题。请帮忙给出正确答案和分析，谢谢！