What does the expression √a + √b combine to?

The expression √a + √b represents the sum of the square roots of two separate quantities, a and b. This expression cannot be simplified into a single square root or another algebraic form that combines the values under one radical sign. Therefore, the most appropriate representation of this sum remains as √a + √b itself.

In mathematics, you can only combine square roots under specific conditions, such as when they are identical or can be factored in a way that allows for simplification. Since √a and √b are generally distinct unless a = b, this expression is specifically retained in its original form.

The other options suggest various combinations or transformations of the original expression that do not hold true in standard algebraic principles.