Obstruction to the flow of CSF at the aqueduct of Sylvius will most likely lead to enlargement of -
All of the ventricles
Only lateral ventricle
Only fourth ventricle
Both lateral and third ventricles
CSF is produced by choroid plexus in the lateral and III ventricles. Then it flows through the aqueduct of Sylvius into the 4th ventricle and from there into the subarachnoid space to be absorbed by the arachnoid
Obviously, any obstruction in the aqueduct of Sylvius will lead to enlargement of the proximal ventricles (i.e. both lateral and IIIrd ventricles).