This diagram helps students identify the key features of a river system, from its source high in the mountains to its mouth at the ocean.

Let's solve the problem step by step.

Task:

Label the parts of a river in the diagram using the given terms:
SOURCE, TRIBUTARY, RIVER BED, MOUTH

The diagram shows a cross-section of a river flowing from mountains to a body of water (like a lake or sea). There are four numbered points (1, 2, 3, 4) with blank boxes next to them that need to be labeled correctly.

---

Step-by-step Analysis:

1. Point 1: Located at the top of the mountain where the river begins.
- This is the source of the river — where the water originates (e.g., from snowmelt, springs, or rainfall).
- ✔ So, label 1 → SOURCE

2. Point 2: At the end of the river, where it flows into a larger body of water (like a lake or ocean).
- This is the mouth of the river — where it ends.
- ✔ So, label 2 → MOUTH

3. Point 3: A smaller stream joining the main river from the side.
- This is a tributary — a smaller river or stream that flows into a larger river.
- ✔ So, label 3 → TRIBUTARY

4. Point 4: The bottom surface over which the river flows.
- This is the river bed — the channel or bottom of the river.
- ✔ So, label 4 → RIVER BED

---

Final Answer:

- 1 → SOURCE
- 2 → MOUTH
- 3 → TRIBUTARY
- 4 → RIVER BED

Now, place these labels in the corresponding boxes next to the numbers on the diagram.

✔ Completed labeling:

```
[ SOURCE ] [ TRIBUTARY ]
\ /
\ /
\ /
\ /
\ /
\ /
V
[ RIVER BED ]
|
|
[ MOUTH ]
```

(Note: The exact positioning of boxes depends on the original layout, but based on the diagram, the labels go as follows:)

- Box near 1 → SOURCE
- Box near 2 → MOUTH
- Box near 3 → TRIBUTARY
- Box near 4 → RIVER BED

---

Summary:

- Source: Where the river starts (top of the mountain)
- Tributary: Smaller stream feeding into the main river
- River Bed: The bottom of the river channel
- Mouth: Where the river ends and flows into a larger body of water

✔ All parts are now correctly labeled!