Why is there "S" been add eventhough after the word usually?

[Elly]

English Language Tests, Intermediate level

ESL/EFL Test #262 "Irregular Verbs Test (10)", question 9

My dog usually ......... her winter coat in the spring. During that time, I have to brush her twice or three times a day.

(a) shed
(b) sheds
(c) shedding

English Language Tests, Intermediate level

ESL/EFL Test #262 "Irregular Verbs Test (10)", answer 9

My dog usually sheds her winter coat in the spring. During that time, I have to brush her twice or three times a day.

Correct answer: (b) sheds

Your answer was: incorrect
My dog usually shed her winter coat in the spring. During that time, I have to brush her twice or three times a day.
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why is there "S" been add eventhough after the word usually?

Elly

[Mister Micawber]

.
'Usually' has nothing to do with the grammar problem. The form of the verb depends on the noun subject. Here, the subject is 'dog' and the verb is therefore 3rd person singular 'sheds'.
.
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Native English teacher at Mister Micawber's