Questions

If some action has started in the past and is still continuing, then present perfect continuous tense should be used instead of present continuous tense. So, the phrase ‘is working’ needs to be replaced with ‘has been working’ to make the sentence contextually correct. Thus, the correct formation would be, ‘Ramesh has been working in this factory for the past three months’.

Astronomy is the study of planets and heavenly bodies. Historically, astronomy has focused on observations of heavenly bodies. It is a close cousin to astrophysics. Succinctly put, astrophysics involves the study of the physics of astronomy and concentrates on the behavior, properties and motion of objects out there.
 

Tooth Enamel is the hardest and most highly mineralized substance in the human body. It is a tissue and not a bone. This tissue has high mineral content which makes it hardest substance.

Femur and Temporal bone of the skull are the hardest bones of the human body.