After dry days, everyone appreciates ______ when there is a timely rain. 

—Don't you think the equipment is worth buying?—Worth buying？I don't think there is________the one we 　saw in the advertisement.

---Susan, go and join your sister cleaning the yard. --- Why ___? John is sitting there doing nothing. 

___ makes me sick that she thinks so highly of herself.

Jack has three sons, and both of _______ are studying in China.