By using all of the digits 9,6,8,7, exactly once

(a) What's the largest 4-digit number you can make?

(b) What's the smallest 4-digit number you can make?

(c) What's the largest 4-digit odd number you can make?

(d) What's the smallest 4-digit even number you can make?

(a) The digits should be at a descending order from thousands place to ones place;

(b) The digits should be at an ascending order from thousands place to ones place;

(c) The digits should be at a descending order from thousands place to ones place based on that the digit 7 should at the ones place;

(d) The digits should be at an ascending order from thousands place to ones place based on that the digit 8 should at the ones place;