Answers and explanation:
A has six significant figures. This is because all nonzero numbers and zeros between numbers are significant.
B has four significant figures. This is again because all nonzero numbers and zeros between numbers are significant.
C has five significant figures. This is because all nonzero numbers, zeros between numbers and zeroes after a decimal and number are significant.
D has seven significant figures. This is again because all nonzero numbers, zeros between numbers and zeroes after a decimal and number are significant.