English grammar?

Question

The restaurant's recently-updated computer system can automatically look up a customer's address when calling to place a take-out order.
A-- can
B--Automatically
C--When
D--Calling to place
E-- No error

I know the answer, I need an explaination

Answer 1

D because it's not the computer system that's calling to place the order.

Answer 2

The subject of the sentence is "the restaurant's recently-updated computer system". If you don't put a subject in front of "calling", it makes it seem like this is the subject of "calling", also. But the subject of "calling" should be "customer". So it has to be:

The restaurant's recently updated computer system can automatically look up a customer's address when the customer is calling to place a take-out order.

Answer 3

First of all, I find it highly unlikely that the restaurant's computer system would be calling to place an order.

Answer 4

D improper verb allocation - an incorrect switch between customer and computer tense.

Answer 5

I don't understand the question. If you don't get any answers you find suitable, feel free to email me, but please explain yourself a bit more clearly.