The correct answers are If an alien lands in your backyard, offer it a cup of tea., If the spaceship is glowing green, it means they come in peace., and If they point a laser at you, you should probably duck.

Zero and First conditionals use present tenses (simple or continuous) in the "if" clause. The result clause can use the present simple (for facts), imperatives (for commands), or modal verbs like will, should, or can (for future possibilities). We do not use will in the "if" clause, and mixing present with past tense (gave) doesn't work here.