simple present vs. present continuous

[Micky]

English Language Tests, Intermediate level

ESL/EFL Test #260 "Irregular Verbs Test (8)", question 5

Every time the family goes shopping, Trish ......... her son push the cart in the grocery store.

(a) let
(b) letting
(c) lets

English Language Tests, Intermediate level

ESL/EFL Test #260 "Irregular Verbs Test (8)", answer 5

Every time the family goes shopping, Trish lets her son push the cart in the grocery store.

Correct answer: (c) lets
_________________________

WHY NOT LETTING?

Micky

[Conchita]

We use the present simple in that sentence because it is a habit or routine. Besides, to form the present continuous, we would need the verb 'to be': Trish is letting.