Countable or uncountable noun?

Điền vào các khoảng trống bằng một từ trong hộp bên dưới ở dạng đúng. Nếu là từ có thể đếm được, bạn có thể cần phải thay đổi nó thành dạng số nhiều.

1. I've faced many challenge  in my life, but none as difficult as this.

2. Some of the best  I heard while I was a student was to take regular breaks when studying so that you don't lose concentration.

3. A dictionary is a wonderful source of .

4. I've made some little for Claire's birthday party.

5. One hundred years ago cars all looked the same but these days they come in lots of different shapes and .

6. My job as a journalist means I can find myself in difficult  at times, but at least it's never boring.

7. There was no  in the remote cottage, so they had to cook over the fire.