16c Did the boy eat his meal? The action verb (eat) must be in the base
17c Nabil, yet his brother, are tall and blond. Yet means in addition
18a I can't walk. I have little energy. We do use (little) with Uncountable noun since the meaning of energy is active
19a I opened the window because the weather was very hot. Because is used for reason
20a The traffic was terrible yesterday. Traffic is U