In the Gulf of Mexico the animals' presence close to shore means their usual habitat is badly polluted, and the crowding could ________ mass die-offs as fish run out of oxygen.
____ we is known to all, English is not very difficult to learn.
The old man had three sons, all of ____ died during World War Ⅱ.
I have bought two pens, ____ write well.
Do you know the reason ____ she has changed her mind?
He failed in the exam, ____ proves that he wasn’t working hard enough.