Learn Spanish (Latin America): Como el descenso es difícil, prefiero usar el trineo. - Since the descent is difficult, I prefer to use the sled.

When stating a cause at the very beginning of a sentence, Spanish requires como. You generally cannot use porque to start a sentence unless you are directly answering a "why" question. If you wanted to put the cause in the second half of the sentence, you would switch to porque: Prefiero usar el trineo porque el descenso es difícil. Causal como is strictly placed at the beginning of the sentence.

Could I use ya que at the beginning of this sentence instead of como?

Yes! You could say Ya que el descenso es difícil, prefiero usar el trineo. Both work perfectly at the start of a sentence to mean "since" or "given that." However, como is often the most common and natural choice for everyday spoken Spanish.

Why doesn't prefiero need a preposition before usar?

The verb preferir connects directly to an infinitive verb without needing a preposition like a, de, or que in between. You simply use the conjugated form (prefiero) immediately followed by the infinitive action (usar).

Would a native speaker use la bajada instead of el descenso here?