[填空题]
$\text { In the following diagram, } \overrightarrow{\mathrm{CA}}=\mathbf{p}, \overrightarrow{\mathrm{CB}}=\mathbf{q} \text { and } \overrightarrow{\mathrm{AD}}=\frac{1}{2} \overrightarrow{\mathrm{AB}} \text {. }$
Express each of the following vectors in terms of $ \mathbf{p}$ and $\mathbf{q} $.
1. $\overrightarrow{\mathrm{AB}}$
2. $\overrightarrow{\mathrm{CD}}$ .
