Learn Portuguese (Portugal): Parece que exibem o esboço, pois é muito valioso. - It seems that they exhibit the sketch, because it is very valuable.

Because parece que is in the affirmative. In Portuguese, stating that something seems to be true expresses a perceived reality, which triggers the indicative. If the sentence were negative (não parece que), it would introduce doubt and require the subjunctive (exibam).

Why use pois instead of porque to mean "because"?

Pois is often used in written or slightly more formal Portuguese to justify or explain the previous clause. While it means the same as porque here, remember that pois can only connect clauses mid-sentence; unlike porque, it cannot be used at the very beginning of a sentence to answer a "why" question.

Why is there no subject pronoun before exibem or é?

Because European Portuguese heavily drops subject pronouns when the context or verb conjugation makes them obvious. Exibem implies "they" (likely the museum staff), and é clearly refers back to o esboço (the sketch). Adding eles and ele would make the sentence sound clunky and unnaturally repetitive.

How is the 's' in esboço pronounced?

It is pronounced like the "s" in the English word "measure" (a "zh" sound). In European Portuguese, an 's' at the end of a syllable takes on this voiced sound whenever it is immediately followed by a voiced consonant like 'b', 'd', 'g', or 'v'.