1.   A. The cracks probably occurred because the layer is too thin.

2.   By painting separate lines on individual sections of concrete, railway maintenance crews will be able to determine where a crack has occurred.

3.   Cracks also can occur in a steel-reinforced slab of concrete.

4.   If a crack does occur, the driver can lose control of the vehicle.

5.   Snecma said its technicians were already on the spot working to find out how the cracks occurred.

6.   The crack occurred where a rivet went through the skin into the stringer, the source said.

7.   When a crack occurs in a hard layer, it is absorbed by the soft layer and does not spread.

8.   When a crack occurs on a piece of concrete, the conductive paint on its surface will be broken or deformed.