Questions & Answers about Туча закрыла солнце.
Because туча is in the nominative case, which is the normal case for the subject.
In Туча закрыла солнце:
- туча = cloud / storm cloud → subject
- закрыла = covered / blocked
- солнце = sun → direct object
So the sentence structure is basically:
- Туча = the thing doing the action
- закрыла = the action
- солнце = the thing affected by the action
In the past tense, Russian verbs agree with the subject in gender and number.
The noun туча is:
- feminine
- singular
So the past-tense verb must also be feminine singular:
- закрыл = masculine
- закрыла = feminine
- закрыло = neuter
- закрыли = plural
That is why the sentence has закрыла.