4. Which length is the shortest?
(2) 2 mm (3) 3 nm
(1) 1 um
(4) 4 cm

1 um is shorter

Explanation:

1 um is equivalent to 1000 nm.

the five characteristics of adolescence are biological growth and development, and undefined status, increased decision making, increased pressure and the search of self.

t = 1/400 h   ⇔ 0.0025 h ⇔ 9s ⇔ 0.15 m

any of the answers are correct.