Generate 30 MC questions for secondary 1 level students in Hong Kong to learn the use of prepositions.
Give the questions in JSON format of an array of objects, each object with the following structure:
{
"question": "I go to school ______ bus.",
"options": {
"A": "by",
"B": "on",
"C": "in",
"D": "to"
},
"correct_answer": "A"
}