Because of the great weight pressing down on them, these layers tend to fold downward at weak spots, and this finally causes an actual break in the crust.
由于巨大的重量向下压岩层，使它趋于在它的薄弱处向下折叠，这最终导致地壳的实质断裂。
2
Don't folddown the corners of the page, it damages the book.
别把书页角折起来，这要把书弄坏了。
3
Once it has arrived at the airport and enters onto the tarmac, it can folddown its electrically powered wings, engage its rear-facing propellor and take off down the runway.