To find the missing statement in Clancy's proof regarding alternate interior angles, we need to consider the geometry involved with the parallel lines and the transversal.
We know:
- \( m∠E = m∠H \) (from the Vertical Angles Theorem)
- The missing statement should logically relate \( m∠H \) with either \( m∠A \), \( m∠C \), or \( m∠D \).
- From \( m∠H \) being equal to \( m∠D \) (since \( m∠D \) is an alternate interior angle to \( m∠E \)), we can conclude that \( m∠D = m∠H \) must be true.
Therefore, looking at the provided options:
- Option 1 \( m∠E = m∠A \) does not relate directly to \( m∠H \).
- Option 2 \( m∠C = m∠G \) does not involve the angles needed here.
- Option 3 \( m∠D = m∠H \) logically follows from \( m∠E = m∠H \) through the properties of corresponding and alternate angles.
So the missing statement must be:
The missing statement is Option 3: m∠D=m∠H.