Critical thinking tests, including those similar in format to the Watson Glaser, split reasoning into small judgments, and each type has its own answer scale.
For an assumption, you decide whether the speaker takes something for granted. Ask: if this were false, would the statement fall apart? If it would, the assumption is made.
For an inference, you rate a conclusion from True to False, with Probably true, Not enough information and Probably false in between. Everyday common sense about how things usually work is allowed; facts the passage would need to state are not.
A deduction follows only if it must be true whenever the statements are. "Likely" isn't enough.
A strong argument is relevant to the question and gives an important reason. A weak one is off the point, trivial, or just restates the question. Keep your own opinions out: a strong argument can be one you disagree with.