Microsoft's current challenges come not only from the Department of Justice and strong competitors in the market, but also internally-the brain drain. In the past 18 months, several heavyweights have left, including technology director Nancy Mai Ford and Silverberg, who led the development of Windows 95, found that they have one thing in common with the reason for leaving, that is, they feel that Microsoft has lost its vitality. Briefly summarize the meaning of this passage. What is the most appropriate? ['Microsoft loses its anger.', 'Microsoft faces serious challenges.', 'Serious brain drain at Microsoft.', 'Microsoft ministers leave the nest.']