Step 1 (Understanding conditional sentences).
Conditional sentences express a situation and its possible result. They generally follow a pattern like:
- If/Unless + present tense, will + base verb (for real situations).
Step 2 (Checking each option).
(a) Incorrect — "If it rains, I am going to the beach" is grammatically possible but unusual in standard first conditional form; it suggests a planned action, not a conditional result.
(b) Correct — "Unless she studies hard, she won't pass the exam" uses present tense in the first part and "will" in the second, matching the first conditional structure.
(c) Incorrect — Should be "if you invite him" (not "would invite").
(d) Incorrect — Should be "When I see her" (not "will see").
Step 3 (Conclusion).
Option (b) is the most correct and standard conditional sentence.
\[
{\text{Unless she studies hard, she won't pass the exam (Option (b)}}
\]