Which statements are true about fractions and ratios? Select all that apply.

Let's evaluate each statement about fractions and ratios:

1. **All ratios are fractions.**
This statement is **true**. A ratio can be expressed as a fraction representing the relationship between two quantities.

2. **Some ratios are not fractions.**
This statement is **false**. Since all ratios can be expressed as fractions, there are no ratios that are not also fractions.

3. **All fractions are ratios.**
This statement is **true**. A fraction represents a part of a whole and can be understood as a ratio between the numerator and the denominator.

4. **All ratios compare wholes and parts.**
This statement is **false**. Ratios can compare two different quantities, which may not necessarily be a part and a whole. For example, the ratio of boys to girls in a class compares two groups.

Therefore, the true statements are:
- All ratios are fractions.
- All fractions are ratios.