A car can have an engine, so this is a has-a relationship.
A teacher is not generally a student, and a student is not generally a teacher. However, a teacher can have a student, or a student can have a teacher. No matter how you look at it, this is a has-a relationship.
A flag is not a color, nor is a color a flag. However, a flag can have several colors, so this is a has-a relationship.
An apple is not an orange, nor is an orange an apple. Likewise, apples don't have oranges, and oranges don't have apples. This is neither an is-a nor a has-a relationship.
A ship is a vessel, so this is an is-a relationship.
A house is a structure, so this is an is-a relationship. A house can also have multiple structures associated with it: a garage, a tool shed, an outhouse, etc. That means this relation can also be seen as a has-a relationship from the house's perspective.
A circle is a shape, so this is an is-a relationship.
Some of the class names in this exercise may have multiple meanings. For instance, we use the shipping-based definition for vessels. However, vessels are also defined as containers like bottles and kettles. If we use the container definition, there is no relationship between a ship and a vessel. The correct answers may vary based on how you interpreted the class names.