What are the conditions imposed on a debt issuer that are designed to protect bondholders called?

Turrubiates corporation makes a product that uses a material with the following standards standard quantity 8.0 liters per unit standard price $2.50 per liter standard cost $20.00 per unit the company budgeted for production of 3,800 units in april, but actual production was 3,900 units. the company used 32,000 liters of direct material to produce this output. the company purchased 20,100 liters of the direct material at $2.6 per liter. the direct materials purchases variance is computed when the materials are purchased. the materials quantity variance for april is: