In each word of the following questions consists of pair of words bearing a relationship among these, from amongst the alternatives, pick up the pair that best illustrate a similar relationship.
16. 

Thermometer : Temperature

A. Millimeter : Scale
B. Length : Breadth
C. Solar Energy : Sun
D. Cardiograph : Heart rate

17. 

Border : Country

A. Pen : Cap
B. Book : Cover
C. Handle : Shade
D. Frame : Picture

18. 

River : Ocean

A. Child : School
B. Book : Library
C. Lane : Road
D. Cloth : Body

19. 

Arc : Circle

A. Number : Count
B. Fraction : Percentage
C. Pie : Slice
D. Segment : Line