Can someone please explain why the correct answer is A to the question below? Shouldn't the home country's demand curve be downward sloping?

When the home country is small, how will a tariff protecting a home monopolist affect the home country's demand curve?

A) There will be an upward parallel shift in the perfectly elastic demand curve.

B) The demand curve will pivot upwards from its vertical intercept.

C) There will be a downward parallel shift in the demand curve.

D) The demand curve will pivot downward from its vertical intercept.