Why does a spacecraft lose direct signal behind the Moon?

Answer: Because the Moon blocks radio line-of-sight to Earth

Because the Moon blocks radio line-of-sight to Earth ✓ — Correct! Radio signals usually travel in near-straight lines, so when the Moon sits between Earth and the spacecraft, direct contact is temporarily blocked.

Because the far side is always darker and colder — Wrong. The far side is not permanently dark. It gets sunlight too. The problem is blockage, not darkness.

Because aliens on the far side mess with the signal — Wrong. There is no evidence that aliens are jamming the signal. The real issue is that the Moon physically blocks the path back to Earth.