To determine which statements about a relation $R$ in first normal form (1NF) are true, let's first understand what 1NF entails. A relation is in 1NF if it adheres to the following rules:

All columns must contain atomic (indivisible) values.
Each column must contain values of the same type.
Each column must contain a unique name.
The order in which data is stored does not matter.

With this understanding, let's analyze each option:

Option A: $R$ can have a multi-attribute key

True. A multi-attribute key, also known as a composite key, is allowed in 1NF. A composite key is simply a key that consists of more than one attribute, and there is no restriction in 1NF against having such keys.

Option B: $R$ cannot have a foreign key

False. The concept of 1NF does not exclude the use of foreign keys. Foreign keys are related to establishing relationships between tables, but 1NF only concerns the atomicity of the values in each column.

Option C: $R$ cannot have a composite attribute

True. A composite attribute consists of multiple sub-parts and is not atomic. Since 1NF requires that each attribute contain atomic values, composite attributes are not allowed.

Option D: $R$ cannot have more than one candidate key

False. There is no restriction in 1NF on the number of candidate keys. A relation in 1NF can have multiple candidate keys.

Therefore, the correct statements about a relation $R$ in first normal form (1NF) are:

Option A: $R$ can have a multi-attribute key

Option C: $R$ cannot have a composite attribute