Holes drilled several kilometers into earth’s crust provide direct evidence about earth’s interior in the form of
a. seismic waves
b. rock samples
c. liquid iron
d. volcanic eruption

Rock samples.

Explanation: Geologists studied and told us that the Earth's crust is composed of various chemicals, minerals, and rock samples. Even the chemicals and minerals are obtained from within the rock samples. Minerals are to rocks such as vegetables are to the salad. These minerals are extracted and processed by geologist and such rock which contains traces of minerals are called ores. 

The investiture controversy began as a power struggle between pope gregory vii (1072–85) and henry iv, holy roman emperor (1056–1106).[2] a brief but significant struggle over investiture also occurred between henry i of england and pope paschal ii in the years 1103 to 1107, and the issue played a minor role in the struggles between church and state in france, as well.by undercutting the imperial power established by the salian emperors, the controversy led to nearly 50 years of civil war in germany, and the triumph of the great dukes and abbots. imperial power was finally re-established under the hohenstaufen dynasty. historian norman cantor: