Oil rated __ only cannot be used in compression ignition engines unless they also carry the __ rating and vice vers a. S;C b. A;B c. A;C d. B; S

## Step 1<br />The problem is about the classification of oil ratings for use in different types of engines. The ratings are S (Service) and C (Commercial).<br /><br />## Step 2<br />The problem states that oil rated 'only' cannot be used in compression ignition engines unless they also carry the 'rating' and vice versa. This means that oil rated 'only' cannot be used in compression ignition engines unless they also carry the 'rating' and vice versa.<br /><br />## Step 3<br />The problem provides four options: a. S;C, b. A;B, c. A;C, and d. B;S. We need to choose the correct option that fits the given condition.<br /><br />## Step 4<br />The correct answer is option a. S;C. This is because oil rated 'S' (Service) can be used in both types of engines, while oil rated 'C' (Commercial) can only be used in compression ignition engines.