According to psychologists intelligence is

Psychologists have proposed several definitions of intelligence, but two components recur across the standard formulations: (a) the ability to learn from experience and adapt to new situations, and (b) the capacity to carry on abstract thinking, i.e., reasoning with symbols, concepts, and ideas rather than only concrete objects. These two components are treated as complementary parts of one construct, not as mutually exclusive alternatives.

Applying this to the item: the stem asks how psychologists define intelligence. Because standard textbook definitions present the ability to learn and the capacity for abstract thinking as jointly necessary rather than as competing descriptions, the accurate answer must include both components together.

A quick check: consider someone solving an unfamiliar problem. They must grasp new information quickly (ability to learn) and manipulate ideas symbolically to work out a solution (abstract thinking). Neither capacity alone explains the intelligent behaviour observed -- both are needed simultaneously.

• the ability to learn (alone) -- accounts for adaptation/learning but omits abstract, symbolic reasoning, so it is only a partial definition.

• capacity to carry on abstract thinking (alone) -- accounts for reasoning but omits the ability to learn and adapt from experience, so it too is only a partial definition.

• either the ability to learn or the capacity for abstract thinking -- wrongly treats the two components as alternatives, when standard definitions require both together.

Hence, the standard, comprehensive definition combines both -- the ability to learn and the capacity to carry on abstract thinking.