how to choose the right answer?

[Jutila]

English Language Tests, Intermediate level

ESL/EFL Test #258 "Irregular Verbs Test (6)", question 3

You have to ......... a lot of water in this part of the country on hot days in the summer months or you could dehydrate.

(a) drink
(b) drank
(c) drunk

English Language Tests, Intermediate level

ESL/EFL Test #258 "Irregular Verbs Test (6)", answer 3

You have to drink a lot of water in this part of the country on hot days in the summer months or you could dehydrate.

Correct answer: (a) drink
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how to choose the right answer?

Jutila

[Mister Micawber]

.
To get the right answer, you must understand that the blank takes an infinitive verb form because it is preceded by the finite verb 'have to'.
.
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Native English teacher at Mister Micawber's