Use "become thinner" in a sentence

1. I follow it farther into the forest, and when I round the bend the trees become thinner, their orange leaves marked by brown blotches

2. For example at 40 years of age the hair shafts become thinner by 5 percent when compared with 20 years ago

3. By now the field is very crowded, and the returns have become thinner

4. He has become thinner and more nervous