Conditionals

Unless

'Unless' is commonly used to replace 'if not' in conditional sentences. For example, 'If you don't study, you will fail' can be rewritten as 'Unless you study, you will fail.' Other words that can replace 'if' include 'provided that', 'as long as', 'supposing', and 'on condition that'. 'Because' shows cause and effect, 'although' shows contrast, and 'since' can show time or reason, but none of these express conditional meaning like 'unless' does. 'Unless' specifically means 'if not' or 'except if'.

Simple present

Both clauses use simple present tense: 'is' (present tense of 'be') and 'go' (present tense). This makes it a zero conditional sentence, which uses simple present tense in both the if clause and the main clause. Zero conditionals express general truths, habits, or situations that always happen under certain conditions. If it used future tense ('will go') in the main clause, it would be a first conditional. Simple past would be used in second conditionals, and present perfect or past perfect in more complex conditional forms.

Had I known, I would have helped.

This is an inverted conditional where 'had' is moved to the beginning and 'if' is omitted. In formal English, we can invert conditionals by putting the auxiliary verb (had, were, should) before the subject and dropping 'if'. The original sentence 'If I had known, I would have helped' becomes 'Had I known, I would have helped.' This inversion makes the sentence more formal and is commonly used in written English. The other options don't show this inversion pattern - they either use normal word order or are not proper conditional structures.

school will be cancelled

The main clause is 'school will be cancelled' because it contains the main result or consequence of the condition. In conditional sentences, the main clause tells you what happens if the condition is met, while the if clause states the condition. 'If it snows heavily' is the if clause (condition), not the main clause. 'It snows heavily' is just part of the if clause without 'if', and 'will be cancelled' is only part of the main clause. The complete main clause includes the subject 'school' and the complete predicate 'will be cancelled'.