Video lesson about Relative Pronouns
Defining (specifying) vs Non-defining (non-specifying) sentences.
Video lesson for Advanced Learners
Some practice will be more than necessary. Here you are some and graded in difficulty :D
PERFECT ENGLISH caters for ordinary sentence construction practice.
OM EXERCISE includes definitions with relatives and sentence formation.
EGO4U includes explanation in English and activities.
AGENDAWEB offers assorted pratice including tests.
Explicación básica en español.