SUCH alone is used with plurals and collective singulars (furniture, luggage, software, information...)
There is often an explicit or implicit comparison: I've never seen such big steaks. I've never seen such big steaks as those served in Texas. Such rare birds are difficult to observe. Why do you have to take such heavy luggage? We don't often get such cold weather in July. Such is life!
SUCH A (or such an) is used for singulars:
Her lipstick was such a violent shade of red (that it looked like blood). Such an event was sure to have repercussions. I've never known such a cold day in July! Why are you wearing such a big grin? What's funny?
SO is either for comparisons or used rhetorically (in implied comparisons).
The sun was so bright (that) I had to cover my eyes. The book was so interesting (that) I couldn't put it down. Wow. That beer was SO good! Mary thinks she's so intelligent!
SO * A has an adjective or an adverb in the place of the asterisk:
So honest a man has rarely reached the heights of government!
This latter form is largely rhetorical and probably best avoided unless you are making a speech. Thus it has not been included in this exercise, except to point it out, when appropriate, as an acceptable alternative.
I've never eaten .......... good food!
so
such
such a
How can Peter afford .......... expensive car?
so
such
such an
John's exam results were .......... good that he was offered places at both Oxford and Cambridge.
so
such
such a
What a rotten hotel. I had .......... hard bed I couldn't get a wink of sleep!
so
such
such a
My bed was .......... hard that I couldn't get a wink of sleep.
so
such
such a
I've never known a hotel have .......... hard beds.
so
such
such a
Why were the children .......... excited last night?
so
such
such a
I've never seen .......... excited children as yours last night.
so
such
such a
Thank you for being .......... kind while I was in hospital.
so
such
such a
Laura was .......... good friend to me when I was in Hospital.
so
such
such a
.......... hard work should not go unrewarded.
So
Such
Such a
.......... remarkable exploit could hardly fail to attract attention.