容器里有多少水（以毫升为单位）？ 答案：___ 毫升

1. Determine the value of one small interval on the measuring cylinder scale

The major markings are at intervals of $10\text{ ml}$. Between $30\text{ ml}$ and $40\text{ ml}$, there are $10$ small intervals.
Value of $1$ small interval = $\frac{10\text{ ml}}{10} = 1\text{ ml}$.

2. Read the water level from the scale

The water level is $4$ small intervals above the $30\text{ ml}$ mark.
Volume = $30 + 4 \times 1 = 34\text{ ml}$.