Scientific knowledge becomes more reliable when it is
biased
questioned
not tested
not observed

questioned

Explanation:

A scientific knowledge becomes more reliable when it is tested. This is because of the fact that framing a scientific question related to the query about the natural phenomena or event can increase the curiosity of finding accurate and reliable results on the basis of implementation of suitable methodology. The evidences based upon the direct observations and data obtained after the scientific procedure can make the scientific knowledge more reliable.  

c is having 4 valence electrons and is bonded to three hydrogens and one sulphur atom, therefore, the number of bond pair is equal to four. as all the valence electrons are used in forming the bonds so, there is no lone pair left on carbon.

s is having 6 valence electrons and is bonded to one other sulfur atom and one carbon atom, therefore, the number of bond pair is equal to 2. as only two valence electrons are used in forming the bonds so, four electrons are left. therefore, two lone pairs are present on s.