12．Li Lei is writing ___________ his pen-friend now．
A．to B．with C．at D．from
13．Going __________ a walk __________ meals is good for our health．
A．for; before B．for; after C．to; before D．to; after
14．—May I come in? --Sorry, _________．
A．you may B．you mayn't C．you needn't D．you can't
15．—_________ are the pens?— Ten yuan．
A．How many B．How much C．How often D．How long
16．Mum, I see dad ___________ football with Mike．
A．is playing B．playing C．to play D．plays
