Commas and semi-colons – solution

Commas
A Alison walked up to her room, opened the door, removed her ridiculous high-heeled shoes and threw herself on the bed.
B For lunch the factory canteen always offers its traditional meatloaf with salad, pasta, baked potatoes with a topping of your choice, cakes, biscuits, yogurt trifle and fresh fruit.
C Robert, the talented but lazy footballer, had not managed to live up to the potential he had shown as a young man.
D So-called experts do at least seem to agree on one point about food, namely that to have a fairly hearty breakfast every day is a sure way of managing to make it to lunch-time without needing to indulge in snacks.

Semi-Colons
E As a middle-aged father of four Andrew Marvell knew well enough the trials of running his own business; after all his first business venture had gone bankrupt after only two years of trading.
F Many readers have written in to the Times complaining of bias in recent articles on Australia; they claim there is evidence of stereotyping in the description of Australians.

These two examples illustrate the fact that often the full stop would serve just as well. i.e.:

E As a middle-aged father of four Andrew Marvell knew well enough the trials of running his own business. After all his first business venture had gone bankrupt after only two years of trading.
F Many readers have written in to the Times complaining of bias in recent articles on Australia. They claim there is evidence of stereotyping in the description of Australians.