If we plot the apparent brightnesses of stars in a globular cluster versus their surface temperatures in a similar way as in the HR diagram , there will be a horizontal branch . Which of the following statements about these horizontal branch stars is wrong ? (A)They have the same absolute magnitude . (B)They have different sizes . (C)Their sole source of energy is hydrogen shell burning . (D)They can help us estimate the distance of the globular cluster from us .

If we plot the apparent brightnesses of stars in a globular cluster versus their surface temperatures in a similar way as in the HR diagram , there will be a horizontal branch . Which of the following statements about these horizontal branch stars is wrong ? (A)They have the same absolute magnitude . (B)They have different sizes . (C)Their sole source of energy is hydrogen shell burning . (D)They can help us estimate the distance of the globular cluster from us .