Six easiest way to get lower abs

1. Warm-Up: Ab Prep
With your knees bent, feet flat on the floor lie on your back. Breathe in and tuck your chin to your chest. Breathe out and slowly curl just your head, neck, and shoulders off the floor as you lift your arms and reach toward your feet. Pause and breathe in. Slowly return to the starting position, breathing out as you go. Repeat eight times.

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2. Roll Up
(A) Lie on your back and stretch your arms and your legs and form a straight line on the floor. Then  Inhale and bring your arms overhead, and begin to curl your upper body off the floor. 
(B) When halfway up, exhale and continue roll forward to reach your toes. Inhale and reverse the move, exhaling halfway down, to return to start. Repeat 10 times.

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3. Leg Drop
(A) Raise your both legs straight toward the ceiling and then breathe in and tighten your abs. 
(B) Exhale and then slowly lower your legs towards the floor till your feet are about four inches above the floor or you can go even lower without lifting the small of your back. Pause and breathe in. Breathe out as you raise your legs to the starting position. Repeat 10 times.

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4. Scissors
Raise both legs straight up towards the ceiling. Firstly lower your left leg until it is six inches off the floor. Lift your head and shoulders and grasp the back of your right leg, gently pulling it toward you. Switch legs and repeat on other side. Quickly complete 10 reps without any pause.

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5. Hip Lift
Raise both legs toward the ceiling and extend your arms on the floor at your sides, palms down. Inhale and tighten your core muscles. Curl your hips toward your ribs as you exhale, lifting your hips off the floor and reaching your feet straight up. Breathe in as you slowly lower. Repeat 10 times

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6. Torso Twist
(A) Sit cross-legged and put your arms out in front of your chest and breathe in.
(B) Slowly move your upper body about 45 degrees to the right while breathing out with your hips square and abs tight. Return to the center and repeat on your left side. Complete 10 reps

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Source : http://health.yahoo.net/articles/fitness/photos/6-easy-lower-abdominal-exercises#1