Answer: Export Cloud Billing data to BigQuery

**Explanation:** Exporting Cloud Billing data to BigQuery is the most effective solution for daily and monthly cost analysis across multiple GCP projects because: 1. **Comprehensive Analysis**: BigQuery allows you to perform complex queries, aggregations, and analysis on billing data across all projects. 2. **Automation**: Once set up, data is automatically exported daily, providing regular cost insights. 3. **Cross-Project Analysis**: You can easily analyze costs across multiple projects in a single query. 4. **Historical Data**: BigQuery stores historical billing data for trend analysis. 5. **Custom Reporting**: You can create custom dashboards and reports using tools like Data Studio or Looker. **Why other options are not optimal:** - **A) Use billing reports in the Console**: While useful, Console reports have limitations for complex cross-project analysis and automated daily/monthly reporting. - **C) Download invoices manually**: This is inefficient, not automated, and doesn't provide the detailed analysis capabilities needed. - **D) Use gcloud billing list**: This command provides basic billing information but lacks the comprehensive analysis capabilities needed for detailed daily/monthly cost analysis across multiple projects.

Author: Rodrigo Sales