A collection has a single-field index on `email`. Which query below CANNOT use that index to avoid a collection scan?

// index: { email: 1 } db.users.find({ email: /^bob/ }) // A db.users.find({ email: "bob@x.com" }) // B db.users.find({ email: { $exists: false } }) // C db.users.find({ email: { $in: ["a","b"] } }) // D