The correct answer is: Only conclusion I follows.
The first statement is an “all” statement, which means that it is true for all members of the group. The second statement is an “some” statement, which means that it is true for at least one member of the group.
The first conclusion is an “all” statement, which means that it is true for all members of the group. The second conclusion is an “all” statement, which means that it is true for all members of the group.
In order for a conclusion to follow from the premises, the conclusion must be true if the premises are true. In this case, the first conclusion is true if the premises are true. However, the second conclusion is not true if the premises are true. For example, if all fishes are grey in color and some fishes are heavy, then it is possible that some light fishes are also grey in color.
Therefore, the only conclusion that follows from the premises is conclusion I.