How exactly is the present perfect used? When do we use past tenses to be polite? What are the differences between at, on and in with expressions ofplace? We can say a chairleg - why not a cat-leg* When can we use the expression do so? When is the usedwith superlatives? Is unlessthe same as ifnot? What are the differences between come and go, between each and every, between big, large and great, or betweenfairly, quite, rather and pretty? Is it correct to say There's three more bottlesin thefridge? How do you actually say 3x4 = 12? And so on, and so on.