The gravitational force between two objects is described by Newton's law of universal gravitation, which states that the gravitational force \( F \) is proportional to the product of the masses \( m_1 \) and \( m_2 \) of the objects and inversely proportional to the square of the distance \( r \) between them:
\[ F = G \frac{m_1 m_2}{r^2} \]
If the mass of one of the objects is doubled (let's say \( m_1 \) becomes \( 2m_1 \)), while the distance \( r \) remains the same, the new gravitational force \( F' \) can be expressed as:
\[ F' = G \frac{(2m_1) m_2}{r^2} = 2 \left( G \frac{m_1 m_2}{r^2} \right) = 2F \]
This means the gravitational force becomes twice as strong.
Therefore, the correct response is It becomes twice as strong.