Questions about stable rank of inductive limit of $C^\ast$-algebras

Question

Let $A$ be an inductive limit of $\{A_n\}$ which are stable rank one. In Huaxin Lin's book An introduction to the classification of amenable $C^\ast$-algebra. The author assume that $\{A_n\}$ and $A$ are unital and $1_{A_n}=1_A$ in the proof of $A$ is stable rank one. (See Proposition 3.2.1 (1) on page 120)

There are two questions:

1. Why it can be assumed that $\{A_n\}$ and $A$ are unital and $1_{A_n}=1_A$?

2. Why is an invertible element $z$ in $A_n$ invertible in $A$?

Can anyone give me a hint to answer these questions?

Thanks!